Aquastat Relay

Alan (California Radiant) Forbes

For some reason, I'm not getting power to the ignition control module on this Hydrotherm boiler. All the safeties (spill, rollout and hi limit) on both legs of the transformer are closed, there's power at B1 and B2 and the light is on on the vent damper. Can I just bypass the vent damper and wire B1 and B2 directly to the ignition control module? I'd make sure the safeties are intact and lock the vent damper open.
If yes, do I need to determine which terminal (B1 or B2) is which? Just for interests sake, how do I do that? Whichever one shows power to ground is "R"?

HomerJSmith

1 & 2 operate the Vent motor- 3 & 4 send power to the ignition module. Alan, you're really smart at this stuff. I'm surprised that you are asking. What is the voltage between 1 & 4 ? Should be 24 V. Between 3 & 4 is a micro switch. Jump 3 & 4 and see if you are getting 24 V at the ignition module. If so just jump 3 & 4 and block the vent open removing power to #1 or just replace the micro switch.

You don't want to eliminate any of the safety devices. Happy Easter!

Alan (California Radiant) Forbes

Yeah, yeah. I'm smart until I'm not.

I want to eliminate the flue damper entirely. I don't like them because I don't understand them.

HomerJSmith

Yes, you could connect B1 to the 24 V on the ignition module and B2 to the 24 Grnd, but you would eliminate the safety rollout switch.

However, you could connect B1 to one side of the rollout switch and still have it in the circuit. Never the less, jumping #3 & #4 would accomplish the same thing.

If you're not getting voltage at the 24 V on the ignition module, check the continuity on the rollout switch. It may be open. If it is open, the vent motor may not be opening the vent and the flame has nowhere to go except out the front of the fire box. The vent damper usually has an indicator telling you the position of the damper-- open or closed.

Alan (California Radiant) Forbes

Thanks for responding, Homer.

I would keep all the safeties on board and just bypass the flue damper.

What does the "Z" terminal on the aquastat relay do?

If you're not getting voltage at the 24 V on the ignition module, check the continuity on the rollout switch. It may be open. If it is open, the vent motor may not be opening the vent and the flame has nowhere to go except out the front of the fire box. The vent damper usually has an indicator telling you the position of the damper-- open or closed.

That's really smart of you to say that. It's my first time on this job as the owner lost patience with the previous tech. As I found it when I showed up, the flame rollout switch wires were jumpered and the fusible link was blown (no continuity). The previous tech. had replaced all the burners and the burner door since they were all fried and the new burner door already had heat damage.

I usually don't see these Hydrotherm boilers soot up, especially on a radiator system, but the first order of business is to clean the HX and then to get the boiler fired.

The guy before me told the owners they needed a new boiler.

As far as the Johnson Controls flue damper, it's stuck open and the light is on, but I don't think the end switch is closed. As you can see on the picture below, there are three relays surrounding the stem of the damper and I don't know which one is the end switch.

HomerJSmith

Since you have 24 V at B1 & B2 at the aquastat, it means that the relay ( K2) in the aquastat is functioning when the thermostat calls for heat. It is an AC circuit, but consider B1 as a powered lead and B2 as the grounded lead. B1 would go to the 24 V on the ignition module and B2 would go to the 24 V grnd terminal.

Z on the aquastat is connected to one leg of the secondary on the aquastat transformer sending 24 V to #2 on the damper. #1 is connected to B2 the other leg of the aquastat transformer. That completes a circuit when K2 relay closes, activating the damper motor.

Between Z & TV should be 24 V.

I don't have a schematic for the damper, but I see a capacitor, resistors and diode, a relay and micro switches and synchronous motor on the board. Usually, I think, when power is disrupted to the motor, it defaults to an open position because the damper is spring loaded.

See this:
https://forum.heatinghelp.com/discussion/179453/old-and-discontinued-mizer-johnson-control-m35ba-1-damper-control-replacement

and:
http://www.graycoolingman.com/uploads/1/0/6/6/10667336/johnson_controls_m35be_vent_damper.pdf

HomerJSmith

The Red & Blue wires attached to the molex plug at the vent damper are #3 & #4. Pull off the molex plug and jump the Red & Blue wires and leave it disconnected from the vent damper board.

The damper should have defaulted to the open position and you should get power to the 24 V connection at the ignition module after you replace the rollout switch (thermo fuse).

When you get it running check the flame and draft.

Alan (California Radiant) Forbes

The end of the story is that we had to replace the aquastat relay as the relay would operate on a call for heat, but would not power up the 24 volt terminals. The previous contractor had jumpered the flame rollout switch terminals and I believe the aquastat relay was damaged by the heat.

I still had to find out why the flames were rolling out, so we took the boiler apart for cleaning. Even though I'd never seen a clogged Hydrotherm heat exchanger, I was convinced there was something preventing proper draw, but it was as clean as a whistle. The only thing that caught my eye was a misplaced baffle which could have restricted the passageways.

We put everything back together and the boiler now works fine - no more rollout.

Steamhead

The problem might be the gas valve, if the built-in regulator got stuck it might not have regulated the flames (via the gas pressure) properly. This could cause overheating. Most times this also causes sooting, but I can see where it might not.

With regard to stack dampers- these can save a significant amount of energy, especially if the boiler is hooked up to an older chimney that was designed for a coal-fired boiler. Some of these chimneys could pull pets and small children up to the roof. With that kind of draft, they will also pull a lot of cold air thru the boiler after it shuts off, cooling it down between cycles. The boiler then has to re-heat on the next firing cycle, wasting a significant amount of gas.

Johnson, Flair and Honeywell no longer make stack dampers. Field bought out Effikal and they are the predominant damper supplier these days. Both Field and most Effikal dampers can be repaired if the motor goes bad, using a replacement Field motor kit, so it makes sense to replace an old, orphaned damper with a Field.

Alan (California Radiant) Forbes

Thanks for chiming in, Frank.

I checked the gas valve outlet and it was within spec. (3.5" w.c.). I also clocked the meter and it was fine.

It is an old brick chimney; don't know if it was ever coal fired, but I did see remnants of an oil supply line. There is also a water heater connected to the same chimney.

If anything, there's not enough draft. I don't have a draft gauge, but I could hardly feel any air movement.

Steamhead

In that case, the chimney needs to be checked. In our company, we refer this to a chimney contractor.

EBEBRATT-Ed

Have a smoke and see if it goes up the draft hood