Basic boiler control questions

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Old 02-21-14, 05:12 AM
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Basic boiler control questions

I'm trying to understand my home's boiler and controls. I believe that I've got the general gist, but at least one thing is confusing me (and maybe I'm wrong about the general gist as well!). So let me ask a few questions:

1. Am I right in thinking that if all the thermostats in the system are removed/disconnected, the boiler should never fire?

2. I believe that when one or more thermostats says that heat's needed (I have 3 zones) by establishing a connection between the red and white wires, this need is conveyed to the boiler, which then reacts. Furthermore, each individual thermostat tells a zone-valve to open. I don't quite "get" how this part works yet. Is the actual idea that the tstats talk to the zone valves, and that any zone valve, when told to open, tells the boiler to turn on?

3. There are two separate things that I can observe from where I stand: the boiler firing, and the circulator pump running. I'm pretty sure that the circulator can run even when the boiler's not firing --- perhaps to "use up" the heat in the boiler rather than have it all gradually escape into the basement area.
Can the boiler ever fire without the circulator running? And who controls the circulator? Do the thermostats do that directly, or does the boiler get controlled by the thermostats, and then the BOILER tells the circulator whether to run or not?

Our overall setup is three zones; each zone returns through a zone valve, and the three merge into a single pipe that goes to the circulator and then the boiler. The output of the boiler has a 3-way branch to supply the three zones. And each zone has its own thermostat. The basic system is probably 60 years old, with a 10-year old boiler, and somewhat newer thermostats.

Thanks in advance for any enlightenment you can bring.
 
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Old 02-21-14, 06:38 AM
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1) Yes, unless you have a domestic how water coil or circuit running off the boiler. In that case the boiler will run to maintain hot water supply in the house.
2) In a zoned system, the t-stats tell the zone valve to open, and when the zone valve opens, it closes a switch which tells the boiler to run.
3) I'll let the pro's go into detail on this one, there are a few ways to control the circulator(s). Most common is the aquastat which also controls boiler temperature.
 
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Old 02-21-14, 06:43 AM
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1. Am I right in thinking that if all the thermostats in the system are removed/disconnected, the boiler should never fire?
Only if you have what is known as a " cold start " boiler. One which is fitted with a SINGLE acting aquastat versus a TRIPLE aquastat that is designed to keep the boiler warm 24/7 ( this is known as a " warm start " system) in order to provide domestic hot water to a home through the use of a 'tankless coil' immersed in the hot boiler water.

2. ... Is the actual idea that the tstats talk to the zone valves, and that any zone valve, when told to open, tells the boiler to turn on?
Yes, that is correct. The thermostat does not communicate directly with the boiler in this scenario. Inside the zone valves are what are called " endswitches " that close when the valve opens. This " endswitch " communicates directly with the boiler. All the endswitches are wired in parallel so that any one will call the boiler to fire.

3. ... I'm pretty sure that the circulator can run even when the boiler's not firing --- perhaps to "use up" the heat in the boiler rather than have it all gradually escape into the basement area.
Yes, the circulator can run without the burners firing. Not so much to 'use up' the heat though...

The boiler is equipped with a 'high limit' control that will turn the BURNERS OFF when that setting is reached. Usually, the setting is 180-190 F . If there is a heat call from one of the zones and the boiler water reaches the high limit setting before the thermostat stops calling for heat, the BURNERS will shut down and the PUMP continue to run. If the heat call continues, the BURNERS may fire again to reheat the water, the PUMP will run the entire time.

Can the boiler ever fire without the circulator running?
The BURNERS can fire without the circulator if your system is WARM START and has a TRIPLE AQUASTAT installed.

And who controls the circulator?
The circulator is typically controlled by the AQUASTAT on the boiler.

Specific answers could be given if you tell us more about the system. MAKE/MODEL of the boiler, MAKE/MODEL of the aquastat and the Zone Valves, whether or not you are heating your domestic water with the boiler or if you have a stand alone water heater.
 
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Old 02-21-14, 10:22 AM
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Thanks...that's great information. I'm at the office so I can't give model numbers, but I can say that the water heater is a completely separate unit sitting near the boiler, so that particular complication is not present.

The zone-valves are Taco 3-wire models; a quick web search suggests to me that they are "571"s -- they sure look like them. And the boiler's a Burnham, installed in 2003. I'll get the P/Ns when I get home.

I asked about the "could the burners fire when all three thermostats are open?" because we've had something weird happen in the last few days: the "downstairs-except-kitchen" loop has been making the whole downstairs hot (like 75 degrees!) even though the thermostat says that the heat isn't on. To be certain of that, I removed the thermostat from its panel, so the two wires (red, white) that come to it are certainly no longer connected. But the fin-coils are still hot. I then thought "maybe something's screwed up and the upstairs t-stat is calling for heat, but it's wired to the downstairs valve", so I removed it, too, from its base. And same with the one in the kitchen. And while all three tstats were sitting on tables next to their usual location, and I was in the basement scratching my head, I heard/saw the burners fire.

The other thing that puzzles me is that the zone valve for downstairs (and the other two as well) appears to be closed (i.e., the little lever that shows me its state is in the "vertical and barely showing" position rather than the "tilted and sticking out more: position). But the pipe above the zone valve is QUITE hot with returning water from the downstairs circuit -- much hotter than the pipes for the other two valves.

Are zone-valves really on/off valves, or are they more like "90% off" valves? I could imagine that I've got gravity-feed circulation happening perhaps...

--John
 
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Old 02-21-14, 10:44 AM
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Hi John,

Post a few pics also if you can...

I'll wait to get more info this evening.

Are zone-valves really on/off valves, or are they more like "90% off" valves? I could imagine that I've got gravity-feed circulation happening perhaps...
Probably quite close to 100% closed... but there is going to be some very minor leaking in almost all types. Certainly not enough leakage to cause gravity flow though.

And while all three tstats were sitting on tables next to their usual location, and I was in the basement scratching my head, I heard/saw the burners fire.
If your boiler is not warm start, then something is messed up with the wiring or one of the zone valves.
 
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Old 02-21-14, 04:12 PM
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Further info/questions

OK. I'm home now, and the boiler is a Burnham 207NCL-TE12. The aquastat seems to be built into the boiler, on the left side when I'm looking into it, along with a low-voltage xformer that seems to power the endswitches, if I'm following the wires correctly.

First, the facts: it's been a warm day in RI -- close to 50 -- but even with all three thermostats disconnected, when I got home the living-room was about 75 degrees. And when I went to the basement to take pics, the burners on the boiler fired up while I was standing there. And (no surprise) the return on the living-room loop was hot to the touch. I'll cut to the chase here: I removed the control-valve activator (the thing with three wires) for the living-room loop, and there was a goodName:  DSC04743.jpg
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Size:  24.3 KB deal of rust/corrosion behind it...and it was clear that the thing that gets pressed in by the actuator was in the "in" position (i.e., "go ahead and flow"). I tapped it with a hammer -- no joy -- and then grabbed it with vice grips and tugged a bit and THUNK!...out it popped.

So that answers one question: the living room was getting heat because its valve was open, even when the tstat didn't TELL it to be open.

What I can't figure, though, is why (a) the boiler was firing up at all, with all three t-stats disconnected, and (b) why, even if it was firing up just to keep itself warm so that it'd be ready to go when needed, the circulator pump was running.

Attached below are a few pictures; I hope they make sense to someone! (Apologies for not un-rotating them.)
 
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Old 02-21-14, 04:51 PM
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OK, that boiler doesn't have an 'integrated' type of aquastat, but still the control scheme is basically the same.

In this picture:



I believe you are going to find that the RELAY above the TRANSFORMER on that 4" utility box (which will unplug if you move that wire 'bail' to the side) is STUCK CLOSED.

There could also be a wiring snafu... do you own a multimeter and know how to use it? I can give you a few fairly simple checks to make if you do.

It's about a $20 part. Honeywell makes them, as well as a number of others. You may find one at a local plumbing and heating supply store. Take the old one with you when you go.

Your zone valve has been messed up for a long time and you didn't notice it because the boiler wasn't acting up. You've probably had minimal gravity flow for a long time.

The corrosion is a result of the top connection leaking for a long time. That green and white stuff is a result of a leak.

If you can't get that cleaned up so if functions properly and the leak repaired, you are probably going to have to have that valve body replaced.
 
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Old 02-21-14, 05:34 PM
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I hate to chime in over the expert, but wouldn't the leak above the zone valve eventually caused the zone valve to get stuck in the open position, resulting in gravity flow. If the zone valve was stuck in, the the zone valve head needed to apply no force to open the valve, so the head and wiring would be just fine. Gravity flow caused the boiler temp to fall, causing the boiler to fire once every so often. This is assuming the boiler is not a cold start.
So I'm not sure why the relay might be bad/ stuck?
 
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Old 02-21-14, 05:38 PM
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1. Yes, I've got a multimeter. I've already checked across screws 1 2 and 3 of each zone-valve, and found no more than a couple of millivolts anywhere -- which is consistent with the idea that at least one of the three wires is floating, since it runs from the tstat to the screw.

2. I'll check on the relay -- good idea. And I like the idea that I didn't notice that problem because the relay wasn't acting up -- makes good sense.

3. I think what I've had was max flow rather than min flow -- the valve was definitely stuck in the open position. Then again, that's the part of the house that probably demands the most heat, so having it heat up whenever upstairs or kitchen demanded it was probably ok.

4. I've got the plumber headed over sometime this month to do some A/C duct work anyhow, and I'll ask him to bring a new zone valve when he comes.

In the meantime, any simple VOM checks you can recommend would be great.

Thanks in advance.
 
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Old 02-21-14, 06:01 PM
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OK, first off, we're measuring AC Volts... I think you already know that...

On the zone valves,

Measuring from 1 to 2 when there is NO call for heat should show ZERO volts.

When the associated thermostat calls for heat, you should see 24 VAC (nominal)

Terminals 2 and 3 are all in parallel, when ANY valve is OPEN you should measure ZERO volts.

When ALL valves are CLOSED (no heat call) you should measure 24 VAC (nominal).

I'm not sure exactly which manufacture you've got on that boiler control, so offhand I can't tell you what terminals to check. Do you have the manual for the boiler handy? Can you tell me whose control is fitted?

wouldn't the leak above the zone valve eventually caused the zone valve to get stuck in the open position, resulting in gravity flow.
Yes, we believe that's what is happening.

If the zone valve was stuck in, the the zone valve head needed to apply no force to open the valve, so the head and wiring would be just fine.
Yes, the zone valve wiring is probably fine. I want to check voltages at the relay to determine if it's stuck closed.

The above checks on the zone valves are just to play the 'safe' card and make sure we're barking up the right tree because a MECHANICALLY stuck OPEN valve body doesn't mean that the endswitch is calling for heat.

Gravity flow caused the boiler temp to fall, causing the boiler to fire once every so often. This is assuming the boiler is not a cold start.
So I'm not sure why the relay might be bad/ stuck?
Boiler IS cold start. SOMETHING is telling it to fire... most likely that relay... but we'll know shortly. Sometimes it's easier to troubleshoot by replacing the relay, but it's not my money!
 
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Old 02-21-14, 06:40 PM
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Check to see if you've got the R8285D control from Honeywell installed. The terminals should match what is shown on this diagram:

Name:  Burnham 2 series schematic.jpg
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(this diagram is for standing pilot, I believe yours is electronic ignition, but the relay control part is the same for both)

Put one meter lead on the " C " terminal.

Other meter lead on " G " terminal.

With NO HEAT CALL you should measure ZERO there. When there IS a heat call, you should measure 24 VAC (nominal) volts.

With ALL THERMOSTATS turned DOWN so NO HEAT CALL, one meter lead still on " C " terminal and the other on the " Y " terminal (probably an ORANGE wire here), there should be ZERO VOLTS.

With NO heat call ( ZERO volts between C and G), if you measure 24 VAC from C to Y , it means the relay is stuck closed.

Give the relay a tap-tap with a screwdriver handle. See if you can 'un-stick' it.

If it was stuck and tapping it un-sticks it, replace the relay. It's a Honeywell R8222U1006 (DISCONTINUED. REPLACED BY R8222U1079), Burnham part number 80160096U

R8222U1079 - Honeywell R8222U1079 - 24 V General Purpose Relay with DPST N.O. switching

Patriot Supply - R8222U1079
 
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Old 02-21-14, 06:56 PM
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I'm still learning: How do you respond with those embedded quotes?

On to the boiler stuff:

With all three tstats still disconnected, I get 0V across terminals 1 and 2 of all three valves, and about 26VAC across terminals 2 and 3 of all three valves.

The boiler control says Honeywell R8285D 5001 (I think -- I had to use a mirror to read it).

I pulled the relay too, a little while ago. It basically gave me an open-circuit reading between every pair of terminals except the two that clearly go to the coil; for those, I got something like 18 ohms, I think.


Then I installed the tstat for the living room loop and set it to 80 degrees. At that point, the reading (on the living-room-loop valve) was 26VAC across pins 1 and 2 (on valve 1, but not 2 or 3) -- , and 0VAC across terminals 2 and 3 on all three valves. So it sounds as if they're doing the right thing.

When I *did* turn on that tstat, the boiler started up -- I heard the exhaust-choke-thing creak open after something like a relay-click, then another relay-click and the burner ignited. Somewhere in there I think that the circulator started as well, but I can't promise that or even say anything reliable about the sequence of events -- I was trying to remember the voltages I'd measured.
 
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Old 02-21-14, 06:59 PM
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You beat me to it!

I'll go do those relay-voltage measurements as well, and let you know what happens.
 
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Old 02-21-14, 07:11 PM
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I pulled the relay too, a little while ago. It basically gave me an open-circuit reading between every pair of terminals except the two that clearly go to the coil; for those, I got something like 18 ohms, I think.
It probably got un-stuck when you pulled it because what you are saying it's doing now sounds correct.

Sometimes when the relay contact get worn they 'weld' together, but it is a VERY light weld, just enough to hold the relay closed. A light tap, or mechanical vibration, like pulling and re-inserting the relay is often enough to un-stick them. They WILL weld again though, so pick up a replacement. I'm betting that's the problem... seen it before a number of times, not all that uncommon really.
 
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Old 02-21-14, 07:37 PM
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I checked the relay voltage readings.

No heat: CG: 0VAC, CY about 4.7VAC
heat call: CG: 25VAC, CY 25 VAC (roughly...can't recall exactly)

So it sounds as if things are more or less right at this point, and I'll pick up a new relay tomorrow as a just-in-case backup measure.

Thanks again for all your help!
 
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Old 02-21-14, 08:27 PM
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No heat: CG: 0VAC, CY about 4.7VAC
That CY should be ZERO. Try pulling the relay and measuring again.
 
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Old 02-22-14, 08:20 AM
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Tried it with the relay pulled -- still 4.7VAC. Then I removed the orange wire that goes off to the vent damper, etc., and it dropped to 0.7VAC. From your circuit diagram, it certainly SHOULD have been zero at that point. With the yellow disconnected because the relay's pulled, and the orange disconnected because I pulled it off the terminal, the "Y" terminal should be floating, right? Of course, maybe it's my cheapo old radio shack first-generation digital VOM screwing up. (Further investigation suggests this is the case. I'll grab my good VOM -- which isn't here in the house -- later today or tomorrow and re-check these numbers.)

I also measured C to the loose orange wire, and got that same 4.7VAC reading. I suppose that it could be coming back through the vent-damper assembly...since that's all it's really connected to.
 
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Old 02-22-14, 08:23 AM
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I also measured C to the loose orange wire, and got that same 4.7VAC reading. I suppose that it could be coming back through the vent-damper assembly...since that's all it's really connected to.
Yes, it could be 'leakage' current from the damper control circuit and of no real issue. In fact, it probably IS.

My concern was that there was some 'crud' between the relay contacts causing the leakage.
 
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