Weil McLain Cga Gold flame error

mark2025

Hello everyone, I’m hoping to gain some insight into an issue we have with our Wel McLain CGa series 2 boiler. This boiler has three zones each with its own control valve. 2 zones are for baseboard heat and one zone is for indirect water tank. This may have been an issue for years but we never noticed it until we had a baby and tried to keep the house warmer.

Problem: Boiler only works properly when it starts a cycle and both zones for baseboard are calling for heat. When both baseboard zones are calling for heat, the system fires normally and continues to cycle normally. The other day I turned up both thermostats to observe and watched 17 start cycles occur and fire the boiler. The moment one of the two thermostats reached temp, the zone valve for that unit would close. The call for heat would continue from the other thermostat still trying to get to temp. At this point, the boiler would attempt to cycle on and fail to light. This is where it enters in to a lockout and eventually resets. By the time (1hr) it resets, both thermostats are calling for heat again and it runs fine. I can also reset it immediately by turning power off to boiler and turning it back on immediately. At this time, it will light the burners on first cycle, but fail on the 2nd or 3rd if both baseboard heat thermostats are not calling for heat. The error happens like clockwork. It doesn’t appear to matter which thermostat is satisfied and which one is calling for heat. The error happens shortly after a good cycle ends and it wants to run the next cycle.
When the error happens, the lights on control module are as follows:

Power: solid light

TSAT: solid light

Limit: solid light

Damper: solid light

Flame: blinking after failure. At the time damper light goes off as well.

When the failure happens, I’ve observed the spark pilot light, and then go out immediately. Burners never fire.

This one really has me scratching my head. The boiler can do unlimited cycles when both thermostats call for heat but fails when one is satisfied and the other calls for heat.

Boiler was installed back in 2016. We have a 3rd Gen Nest for both thermostats. One thermostat has heating and cooling and the other is set for heating only. The heating only was previously an old mercury thermostat. Both are using two wire line for heat. Red/white. When we upgraded the heat only thermostat, our electrician added a transformer for C. (March 2024). I thought this addition may have caused the issue so I reverted back to a basic 2 wire thermostat. Issue still persists. Like I said above, this issue may have been happening since original install but never noticed it until we had a baby and kept the house comfortable for her versus mid 60’s before. It’s more noticeable on cold days because temp drops faster before boiler is reset with power off/on or resets itself.

Thank you for your thoughts and let me know if you need any more info.

Mark

HVACNUT

Any ice build up on the regulator. That will lower lockup pressure. But it's sporadic so likely not the issue.

Lockup and manifold pressures need to be checked.

During the failed ignition attempts, there should be 24 volts between A and C for the pilot, then once pilot is proven, 24 volts between A and B for the main valve. Can you verify?

109A_5

Hello mark2025,

Does your system have a zone valve control module or just zone valves ? System pictures help us help you.

If I understand your description correctly, when both thermostats are calling everything works fine, then when one thermostat drops out and the other is still calling the boiler starts to act up, is that correct ? If things are wired correctly the boiler should never see that transition, electrically speaking.

I would disconnect both thermostats where they are connect to the system and temporarily mimic the thermostat activity with jumper wires (if needed). See if the boiler still acts up or it acts normal.

mark2025

@hvacnut No ice build up on the regulator.

I can give that test a try between A & B. I was home today and monitored the activity. I’m 100% confident that the issue only happens when only 1 of 2 thermostats call for heat. I can reproduce the failure at and time by going from 2 simultaneous calls to only 1.

I did read the manual and one of the faults that can lead to this lockout was labeled as “line polarity is reversed”. I’m not in this trade and talked to an engineering friend of mine. He asked me to take a look at the transformer. He said that the red should be connected to R and the white to C. In my case it is the opposite. The red is connected to C and the white is connected to R. I haven’t done anything with this information yet. Could this be causing the misfire? I traced the red back to module and it is going in to the TSAT port labeled as R in the manual. I’m a little reluctant to think this is the issue because it does fire correctly when two thermostats call for heat but fails when only one calls. I’m not an expert by any means. That’s why I came here. If it by some chance is the cause, it has probably been like that since the beginning. Like I said, we never noticed it because we kept the house pretty cold. I do recall it occurring but never paid attention as when I reset the main power it would kick on because house got cold and both thermostats were calling for heat. Here is a picture of transformer.

109A_5

Yes, typically the Red colored wire is connected to the 'R' terminal, often it does not matter, but it maintains uniformity. In your case with zone valves and NEST thermostats, the wire orientation may be an issue and it all should be review, especially if the boiler works correctly with jumpers as temporary thermostat substitutes.

HVACNUT

If you're using zone valves, which the third party transformer indicates, and if there's a third wire at the Nest, the Common can be connected.

I hate to blame Nest again, but if it truly is happening with only one zone, then...

R could be possibly landing on W at the Nest? we need more pics. Zone valves and thermostat sub base wiring.

mark2025

Yes, using three zone valves. One thing I want to clarify is that the nest in the 2nd level is being fed from two different sets of wire. The AC in attic space is sending a five wire bundle to the nest with 4 of the 5 wires connected at the nest. Y, G, Rc, and C. Inside the wall there is a two wire bundle coming from boiler that is R and W. The other day I checked behind the backing plate to ensure that the R and W feeding from the two wire cable were properly in the Nest Rh and W. They were. Pictures below. The ground level thermostat is currently run by a Honeywell battery powered. I went back to basic thinking it would be a solution and it did not solve the problem. The transformer that powers the zone valves also is connected to the low water sensor (pic also included).

mark2025

I have an extra heat only thermostat. I was thinking of swapping the last nest and having both thermostats be basic to see if things work normally. I’ll report back tomorrow. The house was originally wired for basic thermostats.