A few Weil McLain Boiler questions/issues

[Peter76]

I have a model CG 6-SPDN boiler built in 1994 for my hot water radiant heat (radiators) and will be using it also for radiant floor heating in an addition I am building. It has been running fine without any issues, however, a few weeks ago, it started acting differently.

The boiler seems to try to maintain the "system" temperature all the time, even if no zones are calling for heat. I even turned off the thermostats - and even disconnected the wires from the zone control to the boiler. Once the water temperature drops below 160F, it starts heating. It then heats until the temperature reaches about 200F and then turns off. The temperature limiter in the boiler (the little wheel) is set to 170F. The only way to stop this is to turn off the power to the boiler.

The next issue is that the boiler temperature is dropping by maybe 1-2 degrees a minute, so it starts firing up again about every 30 minutes.

I am not sure if that's how it's supposed to be behaving, what could be wrong, what I could do to diagnose the problem. I would like to see if that is a sign of a boiler failing or if it would probably be something cheap and simple to fix and I can keep my boiler for still a while. Or maybe the boiler behaves how it is supposed to.

thank you

[mlstark]

Could be a few things, I can't give particulars in an open forum, but I don't believe the boiler needs replacement, you should get a tech out there as soon as possible, if you have a runaway boiler the consequences could be severe.

[tinknocker service tech]

like was said call in a pro and get it looked at
that is a good unit and should last quiet a few more years
should not be acting like this so something is wrong

[Peter76]

Before calling someone over the weekend, I decided to look around a bit until I can get an appointment for a pro to come in. What I noticed was that the flow control valve was set to "manual", which means to me that it allows water to flow any time it wants to. The difference in water temperature in the boiler and in the pipes also would mean to me that - due to the different density - water is slowly circulating constantly. Following the manual for the flow control valve, I set it to actually control the flow. Since then, the temperature in the rooms actually does not raise above the set temperature on the thermostat (and the radiators don't always feel hot) and the boiler also doesn't lose temperature that quickly anymore.

It still fires up once it drops below about 160 degrees and heats the water up to 200 degrees. Can it be that the system is actually designed to keep the temperature all the time in case a thermostat would call for heat? In that case, the system would work as designed - although it would not make too much sense to me. And if the system is designed that way, can the system design be changed or would that not make sense?

Basically, my goal is to keep the heating costs as low as possible without replacing the boiler, since I would not want to replace something that actually works and is of quality.

[pacnw]

there are two types of set up on boilers, hot boiler and cold boiler- pretty self explanatory.

also, there could be an issue with the control(s). IF it is set to 170° and it is going to 200°, that control COULD be faulty.

as has been said, call someone who knows boilers and they SHOULD be able to fix the issues as you have relayed them and NOT have to replace the boiler. this is barring any other issues that may be found.

[mlstark]

Peter, the weil mclain gold cgs boiler is a cold start draft induced unit, it doesn't have a low limit to maintain temp, unless you have an indirect tank in the loop for domestic hot water, the boiler is designed to shut off once setpoint has been reached.
I'm going by the info you gave me, but It's hard to diagnose from here, if for 18 years prior it wasn't cycling like this, and now all of a sudden it is, then I think something is wrong.

[skippedover]

Something is calling the burner on. Could be stuck relay or switch and operating off the high limit control, could be a new control installed. You definitely need someone who knows the wiring system to diagnose this expeditiously and effect the least costly repair. Just guessing ain't gonna do that. :whistle: