Intermittent boiler banging, knocking noises

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Old 02-16-15, 08:50 AM
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Intermittent boiler banging, knocking noises

I have an Allied Superhot SG 135 boiler with 6 zones. The boiler is 15 years old and has been making banging and knocking noises. My plumber has changed the pump, the relay, the expansion tank and the aquastat. He has rerouted the cold water feed to the supply side of the boiler from the return side. The boiler has one setting on the aquastat and I have it set at 175 degrees. Its supposed to cycle at 20 degrees of either side of this I believe. However, it generally cycles from about 160 degrees to about 190 degrees. The boiler cycles fine for most of the day but 3 or 4 times a day the boiler is knocking and banging. The odd thing is the pressure on the gauge is fairly constant at 25 to 27 psi always. After reading this forum it seems it should be more like 12 to 15 psi.I have seen the temp gauge go to about 220 degrees when its knocking and banging and psi still at 25 to 27.
I have tried to get the pressure down to 12 to 15 psi by letting water out of the system but it goes back up to the 25 to 27 psi range in a few days. The plumber has asked me to video the boiler making its knocking noises for him to see and hear. I'm giving up on him and hoping this forum might have some insight. Help!
 
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Old 02-16-15, 03:36 PM
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Hi Richard,

You may not have enough flow in the boiler... maybe from day one... (i.e. improperly installed)

From the manual:

NOTE: The boiler should be properly sized for its heating application and maintain an adequate water flow rate during operation. Significantly oversizing the boiler or decreasing boiler water flow rate will cause excessive stage cycling and may result in premature failure of components
For the typical design of 20F difference between return and supply on your boiler, the manufacturer recommends 11.4 GPM of flow. They 'allow' up to a 30F delta across the boiler and this would mean 7.6 GPM of flow.

4.4 CAUTION: WATER REPLENISHMENT
Avoid unnecessary replenishment of system water. It can allow oxygen to enter the system and cause serious corrosion problems. As well, an excessive amount of minerals may be deposited in the heat exchanger. Do not draw water from the heating system for cleaning, flushing, etc.
Any audible sounds in the boiler system may be indications of scaling or lack of sufficient water flow and the system should be checked without delay. Scaling is due to improper maintenance. It is not the fault of the boiler. Scale damage is not covered by warranty.
Please describe your system setup...

You say six zones, I presume these are zoned with electric zone valves and you have one pump for all six zones, yes?

Have you correlated the noises to how many zones are open and calling for heat at the time? If so, is it noisier when only ONE zone is calling, versus MANY?
 
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Old 02-16-15, 03:44 PM
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The boiler has one setting on the aquastat and I have it set at 175 degrees. Its supposed to cycle at 20 degrees of either side of this I believe.
Probably not... what model aquastat is installed? Honeywell L8148E ?

The high limit setting is where the burners should cut off. The 8148 has a 'negative' differential of (probably, there are a few different models) of usually 10F. Some may be 15F. So, the burners would cut off at the setpoint, and come back on at 10-15 below that if the heat call continues.

However, it generally cycles from about 160 degrees to about 190 degrees.
Do you see the 190F when there was a heat call, and that heat call terminated when the boiler was at high limit, or shortly thereafter? It is fairly common for boilers to go PAST the setpoint if the heat call ended (and thus the circulator stopped) when the boiler was at it's hottest. This is generally not a problem... but the burner should ALWAYS cut off right around the same temperature.

The boiler cycles fine for most of the day but 3 or 4 times a day the boiler is knocking and banging.
Is it possible that at these times there is only one zone calling for heat, versus the other times when there might be more than one?
 
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Old 02-16-15, 03:53 PM
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The odd thing is the pressure on the gauge is fairly constant at 25 to 27 psi always.
It sounds as if the pressure gauge may be defective, most are.

Read this:

http://www.doityourself.com/forum/bo...ure-gauge.html

I have tried to get the pressure down to 12 to 15 psi by letting water out of the system but it goes back up to the 25 to 27 psi range in a few days.
Don't keep doing that... note the previous warning about adding water... obviously it's in your best interest to get the problem fixed right...

Your water feed to the boiler should be going through a PRESSURE REDUCING VALVE that drops your city (or well) water pressure down to 12 PSI.

These valves can fail in a few ways; they can plug up and NOT feed ANY water...

or, it's very possible that in your case that pressure reducing valve is LEAKING INTERNALLY and constantly feeding drop by drop of water into the system. Your description of this is very typical of this type of failure.

Does your system also include an INDIRECT WATER HEATER as one of the zones? or do you have a stand-alone domestic water heater?

The plumber has asked me to video the boiler making its knocking noises for him to see and hear.
It actually would be enlightening...

Does the sound begin when the boiler is at it's hottest?

If you can 'visualize' what's happening inside the boiler, would you say that it sounds like small 'explosions'? Think of a pot of tomato gravy on the stove... those bubbles rising up from the bottom... could you envision that being the source of the noise if your boiler was a pot of gravy?

I believe what you are hearing is what we call 'kettling'.

And the cause is almost always scale from the minerals in the water having built up, or improper flow through the system.

Do you know if your boiler system has a BYPASS valve on it?

Can you take and post some pictures of the boiler piping all around?
 
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Old 02-16-15, 07:15 PM
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intermittent knocking banking noises

NJ Trooper I have attached a few pics below.
 
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Old 02-16-15, 07:20 PM
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I actually have 7 zones as the system runs the domestic water. The valves are electric zone valves and one pump runs them all. The noises don't seem to correlate to the number of zones open. It could be one or more. I checked to see if any zones were calling for heat when it started banging. It was a different number each time.
 
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Old 02-16-15, 07:23 PM
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The aquastat is honeywell L4103D. I have attached a pic below. I will watch to see how many zones are calling for heat at the high limit again when its banging.
 
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Old 02-16-15, 07:35 PM
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The cold water feed is going thru a pressure reducing valve that drops pressure to 15psi. You are correct in that my plumber has cleaned it out twice as it has allowed water into the system and pressurized it over the 30 psi rate. Twice it has gone over 30 psi and a valve has allowed water to escape and reduce the pressure. The system heats a water tank. The sound almost always starts when the boiler is at its hottest. The noise I hear is like a hammer hitting metal sharply. They are individual bangs, at the hottest moment. Not sure if it has a bypass valve. I assume to bypass the boiler? Thank you so much for your time!
 
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Old 02-17-15, 04:29 AM
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my plumber has cleaned it out twice as it has allowed water into the system and pressurized it over the 30 psi rate.
That's a separate issue that will probably only be cured by replacing that valve.

The noise I hear is like a hammer hitting metal sharply. They are individual bangs, at the hottest moment.
That would be consistent with 'kettling'. It's either scaled up, or not enough flow. Maybe both... if it was OK for years, the flow may have been marginal, maybe it then got scaled up and now the flow is not enough.

Not sure if it has a bypass valve. I assume to bypass the boiler?
Actually, a bypass for the SYSTEM, allowing more flow through the boiler.

A boiler bypass will reduce flow through the boiler.

I can't tell from the pics if you have one or not.

Look for a pipe going from the hot supply out of the boiler directly over to the return to the boiler, on the system side of the circulator pump. There may be a valve on that pipe... if it's closed, open it.
 
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Old 02-17-15, 07:48 PM
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Hi NJ Trooper,

I had a look for a system bypass pipe and I do not have one. There is a 1" copper pipe that runs from the supply side to the return side but its capped off with a sharkbite. I could have someone connect this pipe to the return side.

I have had the boiler flushed, not sure with what, but they seem to put in an additive whenever they do a routine maintenance.

What do you suggest I do about the scaling? Have my plumber "flush" with a something to take off the scaling?

Appreciate the lesson in boiler maintenance.
Cheers,
Richard
 
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Old 02-17-15, 08:07 PM
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There is a 1" copper pipe that runs from the supply side to the return side but its capped off with a sharkbite.
Someone cut it and capped both ends?

You should have a valve in the bypass... and it should be a SYSTEM bypass, which is different from the BOILER bypass as explained earlier...

Can you show me the capped pipes?

A few folks here have used the Rhomar stuff and had good results:

Rhomar Boiler Chemical Treatment and Test Kit - 83287
 
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Old 02-18-15, 10:36 PM
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Hi Nj Trooper,

attached 3 pics showing copper pipe running along back wall from supply side to return side and then capped off with a sharkbite. Looks like a zone valve was on that line before and it was removed and capped. Pic 3 has a capped pipe with a valve on it that I was thinking of connecting to. Both pipes are the same size.
I will try he Rhomar Boiler Treatment. Is it something I can put in the boiler or should it be done by a plumber? Sometimes I think I know more about this boiler than most of the fellows around my neck of woods. And I know dam little!

Thanks again for your knowledgeable answers!
Richard
 
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Old 02-19-15, 03:23 PM
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Hi Richard,

I'm only seeing Sharkbite caps in the last pic... maybe I need stronger glasses!

I do see a zone valve without a power head on it, what's that about?

Is it something I can put in the boiler or should it be done by a plumber?
I think you can probably handle it. It involves de-pressurizing the system and draining some water and getting the 'juice' into the boiler.

Looking at your pics I don't really see an 'easy' way to get it into the system...

What have you got in the way of hose spigots on the piping? You could get one of those small 'pony pumps' that have hose connections on them. pour the stuff into a bucket and with washing machine hoses pump it in. Then re-pressurize and open all the zones to circulate it.
 
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Old 02-19-15, 05:21 PM
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Hi NJ Trooper,

the line with the missing power head used to heat my hot tub. When the hot tub went kaput the line was capped with a sharkbite. The line went around the back wall and was capped on the supply side of the boiler. I think that the third pic I sent shows 3 lines capped.The top line in the pic is the old hot tub line. I was going to connect the old hot tub line with the capped line that has a valve on it.(see bottom of pic 3)
Was hoping this might increase the flow. I will send more pics as I am not explaining myself very well.

Will try to get the Rhomar in myself and see how it goes. I can't solder, so will get some help connecting those lines if you think its a good idea.
Thanks again,
Richard
 
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Old 03-16-15, 06:17 AM
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still kettling

Hi NJ Trooper,
Back again. The kettling is still happening. Called a plumber to put the descaler in and we had a chat. We live in Vancouver Canada and he says the water is very soft here and boilers don't need descaler. He figures its electrical. The boiler is not getting rid of its heat and the boiler is banging when the water turns to steam.
Is there a way to test the circuit board or the relay to see if the pump is coming on when the zones call for heat? I have a rats nest of wiring and will check all the grommet for connections. Other than that my thought is to force one zone to stay open for a day and see if it stops the banging by increasing flow.

Thanks,
 
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Old 03-16-15, 09:14 AM
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R,
Just a thought. From what I've read I agree with your plumber but it does sound like a flow problem.

When the banging starts is the boiler running or has it reached it's high limit and shut down?

Then as the temp drops the banging stops until the next cycle.

One zone or six zones, if there's no flow and high temp with low water content boilers, kettling could be the result.

Your pump is supposed to come on with a call for heat or hot water and continue to run until everything is satisfied.

What I'm thinking is your pump may be shutting down when the boiler shuts down on high limit instead of continuing to run until the zone valve is closed.

If that happens then flow stops, kettling begins until temp drops by the gravity flow of water through the open zone valves which turns on the boiler again with the pump and the cycle continues.

The bottom line is the pump could be wired wrong. It should run until the tstat is satisfied and not the aquastat.

Leaving a zone open will not help if the pump shuts off on high limit with boiler.

Check to make sure your pump stays running when the boiler reaches high limit.

If not, rewire properly.

If you have a meter and know how to use it check the voltage at the pump when then the boiler reaches limit to see if you still have power to the pump or if it cuts out also, or take a screwdriver and put the metal end on the pump motor and the other end to your ear and listen to see if the pump keeps running.

Good Luck,
 

Last edited by NJT; 03-16-15 at 04:06 PM.
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Old 03-16-15, 12:00 PM
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Have you tried lowering the high limit set point so the boiler water stays at 180f or below, the temperature gauge may not be accurate .
 
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Old 03-16-15, 03:39 PM
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He figures its electrical. The boiler is not getting rid of its heat and the boiler is banging when the water turns to steam.
And that is where Spott is going with the testing of the circulator pump.

It may be that the pump isn't moving enough water... BUT ... and I'm repeating this for the others that may be 'skimming' the messages so they know...

My plumber has changed the pump, the relay, the expansion tank and the aquastat.
This would make it seem to me that the pump itself is probably OK, the temp of 175 that you have set should be fine, the aquastat is new so it should be controlling the pump properly.

It appears that the guy installed a 3 speed pump, WHAT SPEED is it set on?

he says the water is very soft here
Famous last words. How does he KNOW that the water is soft? Just the word of one plumber is not enough to convince me.

edit: What DOES convince me is the various scholarly articles I've just googled up that indicate that you do in fact have EXTREMELY soft water! Less than 0.3 grains per gallon, even lower than the water in my home after being run through an ion exchange softener.

I think you should back up and consider that bypass... if the water is in fact soft, and the Rhomar hasn't helped (did it help at ALL?), and the pump and aquastat are both new, then FLOW would seem to be the problem, based on the facts that we know.

Your guy said:

The boiler is not getting rid of its heat and the boiler is banging when the water turns to steam.
And this is more or less exactly what I've been saying. FLOW.

As I said earlier, your boiler requires between 8 and 11 GPM of flow AT ALL TIMES. What this means is that if only one zone is calling for heat it is highly unlikely, almost impossible, that you are reaching the minimum flow requirement. Two zones and you MIGHT, three zones should be OK.

Saves suggested lowering the High Limit a bit, and that might help, but it's a BAND-AID only, not a CURE. It might be diagnostic though.
 

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Old 03-16-15, 03:40 PM
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Have you told us how long you've lived in the home?

And how long you've had this problem?

Do you know for a fact that there was a time when it did NOT exhibit this problem?
 
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Old 03-16-15, 04:49 PM
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Troop,
What I was wondering was if the pump is wired correctly. If when the boiler shut off on limit if the pump shut off also instead of running until the tstat was satisfied it ran until the limit was satisfied and then didn't come back on until the temp dropped for the boiler again.
As you said everything is new but if it was replaced exactly as it was removed and the plumber never tested it to catch the problem all the new parts in the world will not help.
I would just like him to verify that the pump stays running after the limit shuts off the boiler if the stat is still calling.
I deffinetly agree with you about the flow problem.
 
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Old 03-16-15, 05:13 PM
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I see what you're saying...

Richard, is the pump wired to the C1 and C2 terminals on the aquastat? (Presuming that you have a Honeywell aquastat)
 
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Old 03-16-15, 09:50 PM
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Persistent banging

I shall start at the beginning. House and boiler 23 years old. Boiler heats the domestic water tank and 23 year old water tank died summer of 2014. Plumber replaced water tank with new efficient money saving water tank(hah!) and changed a lot of plumbing pipes to make new water tank fit. No noise heard until heating season when late September early October banging heard. Plumber replaced pump, aquastat, solenoid, expansion tank to no avail. I have since given up on that plumber.
TYpically the boiler starts heating and during the heating rumbling starts and then the banging while water is heating. It subsides when the the heating of the water stops.I have put m hand on the pump to see if it is running and I believe it is as I feel vibration. The pump is set to run at high speed. I have tried the screw driver trick as well but placing my hand on it seems to work fine too. Not sure if the pump is wired correctly so attached a pic. Top black and white wires are for the pump. Sometimes a clicking noise can be heard from the boiler before the cycle starts.I didn't do the Rhomar treatment and i have tried setting the aquastat lower to 175 or even 170 but it doesn't help. Still bangs. You say more flow but is a pipe that is 3/4 inch run from the supply side to the return side enough? Help??
 
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Old 03-16-15, 10:02 PM
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persistent banging

I did say solenoid, probably should have said relay. Attached a pic of what the "relay" looks like that was replaced and a pic of the circuit area where most wires run into.
 
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Old 03-17-15, 12:43 AM
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Trooper is right - the problem is flow.
The aquastat needs flow to monitor the temperature rise of the heat exchanger.
No pump OR bypass means No/Late action from the aquastat.

Wiring note:
It is clear from the ladder wiring diagram that driving the boiler from the end
switches only requires two wires -- any ES(1,2) pair will do -- You just
will not have zone(n) LED illuminated. TH(1,2) is not required, just J1 is.

Instruction E: is for systems with no zone valves -- Ignore.
. . .
E: For Single zone Applications
Install jumper J2 and connect 24 Vac thermostat leads to terminals TH1 and TH2 on Zone 1 plug-in
terminal block.
. . .
 
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Old 03-17-15, 05:56 AM
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Was it when the tank was replaced that the pipes that you believe may have been bypass piping were cut and capped?
 
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Old 03-17-15, 07:41 AM
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R,
How about putting your Black circulator air into C1 and your White wire into C2 where they're suppose to be. or put a meter on the screws where they are now and see if the pump stays powered when the boiler reaches limit.
At present your wires do not look correct to me but that could be my eyes.
 
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Old 03-17-15, 08:27 AM
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persistent boiler banging

The pipes that are cut and capped were done so several years ago when the hot tub was pulled out.
Last night decided to have a full night without hearing the boiler banging so I turned off the power to the boiler the entire night. Turned power back on this AM and 3 zones called for heat. Boiler fired and immediately started banging. The heat cycle was extremely short, maybe 1 minute before it stopped. Boiler did this 3 times and banged each time. 4th cycle was for several minutes and I hear water rushing through pipes. Put my ear to pump and hear a distinct sound of water moving and pipes are now heating up with warm water. Could it be pump is not coming on intermittently and not pushing water through? Banging is water overheating with zero flow? Circuit board looks as if aquastat, pump and relay are all wired to it. This circuit board clicks occasionally before the boiler cycles, could that be an issue?
Thanks for all of the input.
Richard
 
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Old 03-17-15, 08:31 AM
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banging noise

Hi spott,
Was unable to change the wiring for the pump yet. Will try tonight when I get home.
Thanks.
 
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Old 03-17-15, 09:04 AM
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Called a plumber to put the descaler in and we had a chat. We live in Vancouver Canada and he says the water is very soft here and boilers don't need descaler.
i have extremely soft water. i know that because i did my own analysis. My calcium hardness (main contributor to hardness of the water) is 40 ppm and my total alkalinity is 60 ppm. With some other factors my Calcite Saturation Index (CSI) is negative in the range of -0.6 to -1.4 depending on temperature. Which means that my water is acidic when it comes to scaling and deposits and still i had some scaling and kettling going on.

The boiler is 32 yo so i'm not sure if it was descaled at all before. But I ran de-scaler and pump some preventative solution in. That totally fixed the banging that was driving me nuts.

You can find my post around here about my de-scaling adventure.
 
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Old 03-17-15, 09:35 AM
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The heat cycle was extremely short, maybe 1 minute before it stopped. Boiler did this 3 times and banged each time
Please check that the pump is installed in the correct direction.

This would not be the first time that a backward pump has caused hair loss, and it sounds more and more as if this is the problem to me...
 
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Old 03-17-15, 09:41 AM
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How about putting your Black circulator air into C1 and your White wire into C2 where they're suppose to be.
How do you know they're not there already Spott? Do you see something I missed?

Was unable to change the wiring for the pump yet. Will try tonight when I get home.
I wouldn't change any wiring...
 
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Old 03-17-15, 09:48 AM
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Troop,
Looking at the wiring it seems to me the White wire on C1 and the Black wire on first terminal where there is no label
at all and nothing on C2.
At least that's the way it looks to me.
 
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Old 03-17-15, 10:18 AM
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If it's the P1 - P1C , and P2 - P2C terminals you are talking about, I see a black on P1 and white on P1C

I presume those are the pump connections.

Hey, how about the way that MC cable is terminated? That's real classy, isn't it?
 
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Old 03-17-15, 10:36 AM
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Spott,
That is P1, P1C that your looking at ( see controls-2.jpg ) is from the relay powered by CIRC1 pin4 of P1 on the S9361A (Brown wire.)

Wiring diagram: Page 8 MG-SG_Installation_&_Service_Manual_Control_Supplement [pdf]
 
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Old 03-17-15, 11:26 AM
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Some pictures of the pump and the exact model number could help.

Something for latter:
The heat exchanger (image.jpg) is two banks of single pass tube bundles (SG135 = 4/bundle) with each tube seeing 1/4 of the total.
At the rated boiler flow of 11.5 GPM each 1.610" ID pipe has 0.45425 ft/sec at 2.875 GPM,
so air lock is possibility, as is junk settling out on the bottom of the tubes.
 
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Old 03-17-15, 12:10 PM
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Troop, HW,
it's the pic before that one. It's has the C1 & C2 terminals and Rich said it's the top bx cable with Black & White wire is the pump.
Post #22.
 
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Old 03-17-15, 01:03 PM
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Spott, now you've got me completely confused. I don't know where you are seeing C1 and C2.

The terminal strip on the left side, the one with the MC cable next to it... there is no C1 or C2 there.

They are, top to bottom, labeled:

P1 <---BLACK WIRE (presumably pump HOT)

P1C <---WHITE WIRE (presumably pump NEUTRAL)

P2 <no wire

P2C <no wire

L1 <--BLACK wire from improperly terminated MC cable

L2 <--WHITE wire from improperly terminated MC cable
 
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Old 03-17-15, 01:35 PM
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He is looking at the pic in post #22, and There it does look like 1 an 1C due to camera angle.
 
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Old 03-17-15, 02:14 PM
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Right... I got that... and I think he's on a smartphone so that don't help either...

RICHARD,

FIRST THING, check that the pump is not installed backward. It happens more often than even a pro would care to admit.
 
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Old 03-17-15, 10:11 PM
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The pump arrows need to point DOWN for your system.

The pump relay coil is in the same circuit as the boiler LED and will go off and on with the pump.

We do not have a good view of the wiring from the L4103.

I see the pump speed is set on High.
 
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