High Water Pressure, Short Cycling

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Old 11-26-08, 11:30 PM
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Arrow High Water Pressure, Short Cycling

Hello All,

Maybe someone can help me with this issue I'm having.

I have a Teledyne Lars Minitherm Hydronic Heating system with baseboards. 125Jvs(i think)

This house has two apartments and therefore two zones, we purchased this house last year and found the heating system in shambles.

Luckily, we kept a service contract with our gas supplier and when our circulator motor died they replaced it under the contract. Unfortunately, they do not cover the plumbing aspect, just the boiler and motor.


The two zones were wired with the upper apartment calling the boiler for heat and the lower apartment activating a zone control.

Therefore, our thermostat needs to call for heat before they would receive any heat. The fun side of this story is, the lower apartment's thermostat was controlling the upstairs zone valve.

The person living downstairs kept wondering why they had all this heat and we were wondering why it wouldn't heat up upstairs.

*Sigh.*

After looking over the system, I made a few changes. I rewired the zones to a taco 3 zone controller and rebuilt both zone motors, so when our thermostat calls for heat, we get it and ditto for the tenant.

I found that a few of the air bleeders were closed and if opened, leaked - so I replaced them.

When we had the yearly service call in to startup the system and clean it, the technician mentioned the pressure was a little high.

It was sitting at 30psi. Okay, the tech recommended turning the intake valve pressure down, but he could not do it (no plumbing covered) and to open the air bleeders.


After doing this, I found that when the system is idle, the psi will sit around 20psi or so, but when it heats up, it will jump back up to 30psi and the relief valve will leak a little bit.


At the same time, the system seems to be short-cycling (180f) it will come on, work for a minute or two and switch off.

After reading some of the posts, I'm inclined to check my expansion tank, but exactly how to do this, I still am unsure of.


Is there anything that causes a system to have high pressure and also short cycling?



--
I'm also intending on installing a single coil hot water tank as a third zone, any suggestions?



Thanks in advance

 
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Old 11-27-08, 12:31 AM
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You need to check the pressure when the temperature of the boiler water is at room temperature. Unless you have a high building (in excess of three stories) the pressure at room temperature should be about 12 to 15 psi. If your pressure is higher at that temperature you need to first turn off the manual valve in the fill piping and then using the boiler drain let out enough water to lower the pressure to the 12-15 psi point.

Now open the valve you previously shut and listen carefully to determine if water is flowing into the system. You may want to use a screwdriver with the point on the fill valve and the handle against your ear. If you hear any water flowing then either your "make-up" pressure reducing valve (PRV) is misadjusted or leaking. If the water is flowing then turn off the manual valve.

Monitor the boiler pressure for the next few hours (boiler still off) and see if the pressure drops. If it does then you have a leak and you need to find the leak and repair it. If there is no change in the pressure then go ahead and turn on the boiler and allow it to come to temperature. The pressure should be somewhere between 15 and 25 psi. If it is higher, then you have an expansion tank problem.

Pictures of the boiler and piping will help diagnose any problems. To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected.
 
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Old 11-27-08, 08:39 AM
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Monitor the boiler pressure for the next few hours (boiler still off) and see if the pressure drops. If it does then you have a leak and you need to find the leak and repair it. If there is no change in the pressure then go ahead and turn on the boiler and allow it to come to temperature. The pressure should be somewhere between 15 and 25 psi. If it is higher, then you have an expansion tank problem.
...and this is where I am at. I was able to adjust the PVR valve for the water intake and the system seems to be fine at 15-20psi (with both zones open) but if I start to run the system, it will spike up to 30 when heating. If it's been idle for a bit it will come back down.

I am thinking expansion tank issues (?)

I will post some pix later on today.

 
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Old 11-27-08, 11:29 AM
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I am thinking expansion tank issues (?)
Me too .

What type of tank ? bladder or compression ?

The cold pressure shouldn't really be above 15 PSI ... you adjusted the feed regulator ... how did you do that? did you drop the boiler pressure to zero with the boiler cold and let the valve fill the system? Remember that the regulating valve can't DROP the pressure, only increase it ... so the system pressure could well be above the setting of the valve already ... you need to manually drop the pressure and let the valve bring it back up ...

While 20 is not really too high, it does limit the 'headroom' that the expansion tank has available. Let's say you start at 20, and the pressure increases 7 PSI from cold to hot ... now yer at 27 and too close to the opening point of the relief valve. If you start at 15 and rise to 22 ... no problem ...
 
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Old 11-27-08, 11:42 AM
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the system seems to be short-cycling (180f) it will come on, work for a minute or two and switch off.
Those MiniTherms are very sensitive to boiler flow ... it's a copper tube heat exchanger in there ... They are designed to operate with a temperature difference of 20 between the supply and return, but between 10 and 30 is allowable ... although you should strive for the 20 ...

They are also to be piped with a SYSTEM BYPASS valve ... let's see the pics and go from there ...
 
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Old 11-27-08, 03:25 PM
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Ok here are some pictures, as you may see, there is no bypass valve.







 
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Old 11-27-08, 04:55 PM
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Pressure

Let's check the air charge in the bladder type expansion tank.

Turn off power to boiler.

Close manual feedwater valve.

Attach garden hose to any drain on the system... that one on the return line is easier to get to than the boiler drain on the bottom...

Watch pressure gauge on boiler and open the drain valve.

...repeat loop start...

Let boiler pressure go to zero, and close drain valve.

Using an accurate tire pressure gauge, measure the pressure on the valve under the black cap on the red expansion tank.

If it's less than 15 PSI, put air in with a compressor or bicycle pump until it's between 12-15 PSI ...

Look at the boiler pressure gauge. If it has 'lifted' off zero after adding pressure to the tank, go to ...repeat loop start...

Else, continue...

If you hear anything that sounds like air is escaping from the tank and bubbling into the system, it may be just that if the bladder inside the tank is ruptured.

If all is well, after repeating the above steps, you will have zero PSI in the boiler and 12-15 PSI on the tank.

OK... at this point, open the manual feedwater valve and watch the pressure gauge. It should rise and stabilize after several minutes to between 12-15 PSI. If it goes above 15, back off the adjusting screw counter-clockwise a half to a full turn.

Drain the pressure from the boiler and let the valve bring it up again ... if still too high, back off the screw a little more ... lather, rinse, repeat, until pressure in boiler is around 15 PSI cold.

If you have to replace that tank, yer gonna have fun, cuz there aren't any valves to isolate the tank. Looks like you'll have to drain...
 
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Old 11-27-08, 05:05 PM
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Short cycling

Yer right... no bypass ... bummer ...

With two 3/4" heating circuits, of which only one might be active at a time, you might have either or both of:

Too fast flow in heating circuits (can you hear the water flowing?)

Not enough flow in boiler. (could easily contribute to short cycling problem)

Adding a system bypass would solve the boiler flow issue, and probably solve any issue with too much flow in the circuits.

I believe the heart of the short cycling problem is the fact that it's a large boiler, and a light heating load. There's just so much heat you can pump through a 3/4" loop ... about 40K BTU ... so if only one zone is calling, your boiler fires up and hits high limit quickly ... you can't extract the heat as fast as it's being put in ... so it's bouncing off the high limit.

How to solve ? ummmmm... Beckett Heat manager MIGHT help ... it would widen the differential a bit and you would get slightly longer cycles, farther apart ...
 
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Old 11-27-08, 07:42 PM
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Originally Posted by NJ Trooper View Post
Let's check the air charge in the bladder type expansion tank.

Turn off power to boiler.
-----

If you have to replace that tank, yer gonna have fun, cuz there aren't any valves to isolate the tank. Looks like you'll have to drain...
Okay Nj Trooper,

I've turned off the system and drained it until the pressure sat around 5 psi or so (I'm guessing the water in the system vs gravity) and tried to release the valve on the expansion tank ... nothing, no air, nothing.

Ok, so I checked with a tire gauge and same deal.

I went and grabbed my portable inflator (I don't have a bike pump) and set it to inflate..... nothing - no added pressure, no air going into the system - I even opened the drain while pumping to see if it would help, nada.

I wanted to figure out what kind the expansion tank was so
I turned it and heard water sloshing around in it.

From what I can recall, the membrane is to separate the water from the air so... unless air got into the expansion tank... the bladder is toast?


Like I said though, no air, no water from the top valve.

Any ideas?
 
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Old 11-28-08, 08:03 AM
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Well, I think i have my work cut out for me.

  • I'm going to replace the expansion tank.
  • I'll throw a bypass between the intake (after the circulator) and the outlet (before the zones) - is this right?
  • I'm looking at the intellicon-hw manager

Finally, I want to throw an indirect hot water tank on a zone. I currently have a 60 gallon 3800w tank there and was wondering what would be a good replacement.
 
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Old 11-28-08, 12:30 PM
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I would hold off on the bypass just yet ... and we'll talk about the indirect later... right now, you wanna get that heat going ... it's been working all these years without the bypass ... right ? and your hot water heater is working ... yes ? But, it's gettin' cold out, so why not let's forget about those "while I'm at it" jobs, because they can be like opening a can of worms.

So let's get that tank replaced first ...

Before you install the new tank, verify the air charge to be 12-15 PSI ... and adjust if necessary.

While you are out picking up the tank, also pick up a 1/2" ball valve, and a short 1/2"thread pipe nipple.

You thread the nipple into the elbow that the tank was on, thread on the ball valve, and thread the tank into the ball valve. Oh, pick up some teflon tape and/or some rectorseal #5 too ...

This way, the NEXT time you have to change the tank, you won't have to drain as much water ... drop the pressure, close the valve, spin off the tank ...

If your gauge did not go to zero, and sat at 5 PSI, there's a real good chance that gauge is outta whack too ... should go all the way to zero, the camera might be adding 5 PSI ... so maybe that 20 that you see is really 15 ? and OK ?

You need to verify the pressure gauge before you go much further after replacing the tank. Maybe replace the gauge at the same time ?

furd likes to see relief valves replaced every five years ... I kinda tend to agree ...

Those are things I would do before thinking about the bypass and the water heater ...
 
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Old 11-28-08, 01:57 PM
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Talking

Originally Posted by NJ Trooper View Post
I would hold off on the bypass just yet ... and we'll talk about the indirect later... right now, you wanna get that heat going ... it's been working all these years without the bypass ... right ? and your hot water heater is working ... yes ? But, it's gettin' cold out, so why not let's forget about those "while I'm at it" jobs, because they can be like opening a can of worms.

So let's get that tank replaced first ...
Done

While you are out picking up the tank, also pick up a 1/2" ball valve, and a short 1/2"thread pipe nipple.
Dammit. I isolated the boiler itself by closing the intake and the zones and the tank came right off. Hmmm.... maybe when I go to plumb the bypass I'll do that too.

If your gauge did not go to zero, and sat at 5 PSI, there's a real good chance that gauge is outta whack too ... should go all the way to zero, the camera might be adding 5 PSI ... so maybe that 20 that you see is really 15 ? and OK ?

You need to verify the pressure gauge before you go much further after replacing the tank. Maybe replace the gauge at the same time ?

furd likes to see relief valves replaced every five years ... I kinda tend to agree ...

Those are things I would do before thinking about the bypass and the water heater ...
After changing the tank the system seems to be sitting at a steady 20psi (the tank came 12psi precharged) - so you may be right, the camera may have added 5 pounds.

When the tank came off it was full of staining black rubber pieces like you'll get when rubber starts to decompose.

Thank you all for your input.Beer 4U2Beer 4U2

I'll be attacking the next part in short order - I really need to change my hw tank though - it keeps tripping breakers as it was installed with undersized elements :O

Any suggestions on the indirect hw tank?

 
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Old 11-28-08, 04:58 PM
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Which Indirect ? Xiph ? Who ?

OK good so far!

I'm not too awful hip on the various indirects available ... there's lots of them ... not too product smart here ... some of the other guys will jump in with suggestions ... I think the concensus is the Triangle Tube ... which I believe is the same one Weil-McLain sells as their brand rebadged.

On the bypass...

Manf recommends that it be a full size bypass, meaning the same size as the large supply pipe off the top of the boiler.

There needs to be a valve on that line, and it really should be a valve designed for throttling ... ball valves are not ... GLOBE valves are ...

You could tee into that large supply line, run to the left, down to that rusty return pipe between the valve and the pump. The bypass needs to be installed on the SYSTEM (not the boiler) side of the pump.

Maybe you could replace that section by the pump with copper, and put a tee right there.

You should also install a thermometer on the return to the boiler. Using the gauge on the boiler, and the one on the return, you would set the opening of the bypass valve for the correct temperature difference across the boiler.
 
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Old 11-28-08, 05:06 PM
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Topic drift...

I don't wanna drift too far, but wanted to comment on something you said about your electric water heater.

If the elements are only 3800 Watt, there would be LESS current drawn, and LESS likliehood of tripping a circuit breaker. I suspect you've got a 'soft' breaker there.

I was gonna mention the wire going to the heater ... That really should be 'fixed up' ... I like the little 'squiggles' of wire up overhead there ... the wire is not only too long, it's the wrong type.

If'n I were you, I'd replace that with type MC (armored metal) cable, just like the stuff on the boiler.

What gauge is that wire ?

What size breaker runs the water heater ?
 
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Old 11-30-08, 09:38 PM
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Just wanted to follow up - the expansion tank replacement fixed the high pressure issue (and it doesn't seem to short cycle as much anymore).

One indication I found that the expansion tank was dead, was the black dye (from the bladder rubber {heh}) that came out of the lowest drain off the boiler.

This is the same black dye you'll find in toilets when the seals start to go.


Originally Posted by NJ Trooper View Post
I don't wanna drift too far, but wanted to comment on something you said about your electric water heater.

If the elements are only 3800 Watt, there would be LESS current drawn, and LESS likliehood of tripping a circuit breaker. I suspect you've got a 'soft' breaker there.
This could be, however, the tech who checked it originally said the elements were in fact undersized for the hw tank - BS in my opinion.

I was gonna mention the wire going to the heater ... That really should be 'fixed up' ... I like the little 'squiggles' of wire up overhead there ... the wire is not only too long, it's the wrong type.

If'n I were you, I'd replace that with type MC (armored metal) cable, just like the stuff on the boiler.

What gauge is that wire ?

What size breaker runs the water heater ?
Oh gosh, they did everything wrong with the hw heater... (and actually everything else too)

Originally it was a gas hw tank, but I suspect the utility shut that down noting the chimney as the only vent and determined it was only good for the boiler.

This is why we are looking at installing the indirect - to save money and clear up that nonsense.
 
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