Help with Weil-McLain CGa gas boiler?

Jaaan

Here's the manual for my boiler: https://www.weil-mclain.com/sites/default/files/field-file/CGa Series 3 Boiler Manual 0520.pdf

This boiler has been mostly fine since we moved in last year. Over the last couple weeks, we've occasionally been waking up to a cold house, with the lights on the control module flickering erratically (not like any error code from what I can tell). See YouTube video here for example: https://youtu.be/W4E-Kigkn_M

The TSTAT/CIRC and LIMIT lights flicker on and off. Then they stay on as DAMPER and FLAME come on, but then TSTAT/CIRC and LIMIT flicker off again and everything turns off. Then the cycle repeats.

What I've been doing to resolve: I just turn the boiler off and step away for an hour. This is around 5am or so. Around 6am, I go back and switch the boiler on and it starts more or less working normally. I'll see the TSTAT/CIRC and LIMIT lights trip and turn off from time to time but it's an isolated incident during the daytime—it's only during the cold nights that it won't leave that cycle and create heat at all.

I've done the basic stuff suggested by my HVAC pro like cleaning the flame sensor and leaving the damper stuck open. Any suggestions?

HomerJSmith

TSTAT/CIRC and LIMIT lights are not suppose to flicker. See chart 2. What kind of thermostat do you have and how many? Make and model of zone valves and how many? Pics also help.

EdTheHeaterMan

Also the YouTube link did not work. Try using the actual address of the video.

EBEBRATT-Ed

Sounds like possible some loose or corroded wiring connections. Is the basement damp?

Jaaan

YouTube link should be fixed, thanks for that. Video probably will need to be fullscreened in HD for it to be legible...

Here are some additional photos of my setup and Taco 007 circulators: https://imgur.com/a/G54nHDr

That's a Taco SR502-4 2 Zone Switching Relay on the wall.

For thermostats, the house came with a Vive Comfort TP-N-701 (controls one side of the house) and a Honeywell TH8320R1003 (controls the other side). Are either of those known to be problematic? Fella in this video I found had a similar issue with the TSTAT/CIRC light flickering that came back to how his Nest thermostat had been wired.

Jaaan

EBEBRATT-Ed said:

Sounds like possible some loose or corroded wiring connections. Is the basement damp?

No moisture in the basement but good point on the loose/corroded connections.

109A_5

Hello @Jaaan,
I would try re-seat all the connectors on the control module. To me (looking at the LED pattern) it looks like it is either intermittently loosing the TSTAT call or the Limit circuit has a loose connection so it just keeps shutting down. And then the cycle has to start all over again from the beginning.
It never seems to get to this point (manual text below) which is why I think the TSTAT or Limit is failing intermittently. It seems to drop out a lot faster than 15 seconds. Sometimes it does not even get to the ignition stage. Assuming NG, LP is a bit different but still 15 seconds.



I would also try temporary bypassing the Taco SR502-4 2 Zone Switching Relay unit to eliminate that by connecting the two black TSTAT wires at the boiler (wire nut connections in Red box in drawing). See if the symptoms change or go away.



If the symptoms remain the "Limit" circuit should be verified. Also see Troubleshooting Chart 5 and Chart 6 on manual pages 55 and 56.

If the symptoms go away with the Taco SR502-4 2 Zone Switching Relay unit bypassed it may be at fault.

Jaaan

109A_5 said:

Hello @Jaaan,
I would try re-seat all the connectors on the control module. To me (looking at the LED pattern) it looks like it is either intermittently loosing the TSTAT call or the Limit circuit has a loose connection so it just keeps shutting down. And then the cycle has to start all over again from the beginning.
It never seems to get to this point (manual text below) which is why I think the TSTAT or Limit is failing intermittently. It seems to drop out a lot faster than 15 seconds. Sometimes it does not even get to the ignition stage. Assuming NG, LP is a bit different but still 15 seconds.



I would also try temporary bypassing the Taco SR502-4 2 Zone Switching Relay unit to eliminate that by connecting the two black TSTAT wires at the boiler (wire nut connections in Red box in drawing). See if the symptoms change or go away.



If the symptoms remain the "Limit" circuit should be verified. Also see Troubleshooting Chart 5 and Chart 6 on manual pages 55 and 56.

If the symptoms go away with the Taco SR502-4 2 Zone Switching Relay unit bypassed it may be at fault.

Much appreciate this. Thank you. Checked al the connectors on the control module and they seem totally secure.

Last night, I woke up around 1AM to the boiler trying in vain to turn on and the TSTAT/CIRC lights flickering as before. Turned it off and turned it back on at 5am and it worked fine. House is warm now.

Didn't see your comment before, so I will wait for tonight when it starts to fail again and I will try bypassing the Taco unit to see what the results are.

Probably would have hired a pro to come check it out by now but the problem only really manifests during the night!

109A_5

Jaaan said:

Checked al the connectors on the control module and they seem totally secure.

Ok, what I meant by "re-seat all the connectors" (with the power off BTW) was not that they were not secure in place, but sometimes connector contacts oxidize and disconnecting them and reconnecting them wipes away the oxide layer and reestablishes a normal connection.

Do you do a nightly setback or does your boiler room's temperature change much ? Another thing you can do is if you suspect the control module has a thermal intermittent. Is when it is acting up without shutting off the power like you normally would for an hour. Take a hair dryer and warm up the control module a bit and see if it comes back to normal operation. Don't bake it just warm it up a bit.

Jaaan

109A_5 said:

Jaaan said:

Checked al the connectors on the control module and they seem totally secure.

Ok, what I meant by "re-seat all the connectors" (with the power off BTW) was not that they were not secure in place, but sometimes connector contacts oxidize and disconnecting them and reconnecting them wipes away the oxide layer and reestablishes a normal connection.

Do you do a nightly setback or does your boiler room's temperature change much ? Another thing you can do is if you suspect the control module has a thermal intermittent. Is when it is acting up without shutting off the power like you normally would for an hour. Take a hair dryer and warm up the control module a bit and see if it comes back to normal operation. Don't bake it just warm it up a bit.

Don't do a nightly setback but the temperature in the boiler room does get pretty low at night. There's no outlet for the heat in the basement so the room doesn't really get heated... our home inspector mentioned that he recommended we add that.

Good call re: the hair dryer. I was going to do something like that with a space heater but hair dryer makes much more sense.

This morning I checked on the boiler and only the power light was on, no TSTAT/CIRC or LIMIT or other lights, even though both zones were calling for heat and all the correct lights were on on the Taco unit. I connected the two black thermostat wires as you indicated and successfully got heat going with no issue.

109A_5

Hello @Jaaan,

Jaaan said:

This morning I checked on the boiler and only the power light was on, no TSTAT/CIRC or LIMIT or other lights, even though both zones were calling for heat and all the correct lights were on on the Taco unit. I connected the two black thermostat wires as you indicated and successfully got heat going with no issue.

Seems like your problem is related to the Taco SR502-4 2 Zone Switching Relay unit OR the wires and /or connections between the Taco SR502-4 2 Zone Switching Relay unit and the Boiler.
You may want to verify the low voltage connections in the Taco SR502-4 2 Zone Switching Relay unit. Be careful there is 120 Volts in there.

Edit: When you shut the Boiler off for an hour does it also shut off the Taco SR502-4 2 Zone Switching Relay unit ?

Jaaan

109A_5 said:

Hello @Jaaan,

Jaaan said:

This morning I checked on the boiler and only the power light was on, no TSTAT/CIRC or LIMIT or other lights, even though both zones were calling for heat and all the correct lights were on on the Taco unit. I connected the two black thermostat wires as you indicated and successfully got heat going with no issue.

Seems like your problem is related to the Taco SR502-4 2 Zone Switching Relay unit OR the wires and /or connections between the Taco SR502-4 2 Zone Switching Relay unit and the Boiler.
You may want to verify the low voltage connections in the Taco SR502-4 2 Zone Switching Relay unit. Be careful there is 120 Volts in there.

Edit: When you shut the Boiler off for an hour does it also shut off the Taco SR502-4 2 Zone Switching Relay unit ?

Yes, it does also shut off the Taco.

EdTheHeaterMan

From everything I am reading here, it appears that the Taco SR502-4 has a bad relay contact or a bad solder joint on the printed circuit board. In either case the Taco Zone Control should be replaced, unless the homeowner is handy with a soldering Iron on electronic devices. To verify this before replacing the Taco Control you might try replacing the wire that connects the Taco to the Boiler indicated by the purple wires on the diagram.


The fact that temperature might be a factor in this problem leads me to believe that a metal connection is failing during colder conditions. Since metal can expand and contract with temperature change, you want to eliminate the lower cost metal first. A new piece of thermostat wire is less expensive than a Taco Zone control. And wouldn't you feed bad after changing the expensive control and find that you did not solve the problem of a defective piece of wire.

Mr Ed.

Mad Dog_2

Like Timmie Mac always taught us go over over all your grounds too!  I always gazed at those circuit boards in wonderment, but the times I saw Big Joe Carraher (Tank Mechanic 11th Cav. Vietnam, counterman, electronics savant!  & Co-Owner at Christ Plumbing Supply (est. 1810) New Hyde Park NY ) trace them out and then resolder the break, it became less vexing to understand 😉.   Mad Dog.