GAs Boiler Restart

JLFT

Our Peerless MI04 Gas Boiler has been experiencing main burner flame shutdown during the Boiler Demand signal from the Tekmar 260 Control Unit (Boiler Demand pointer ON, Circulation Pump symbol ON). The circulation pump continues to run and the flue damper remains in the OPEN position, but there is no flame. I am able to shut off power to the 260 and the boiler including pumps, can wait 5 minutes and then repower to begin heating again which will continue normal operation for 4 to 48 hours before main burner shutdown again.

I have thoroughly tested all Tekmar Demand input and output signals and functions (eg. Boiler Demand Targets for DHW and Heating). No problem I can detect with Tekmar.

From the Boiler Troubleshooting section of the Peerless Boiler Manual there are about 10 possible causes of the flame shutdown. 1) The "Flame Rollout Switch remaining open" is not the shutdown cause since it is a “non-recycling switch” which requires replacement once it has been activated. 2) The "Blocked Vent Switch remaining open" is also not the shutdown cause since it requires a manual reset if activated which has not been required since I can restart heating after waiting 5 minutes. There are a few other causes which I am unable to assess, such as the Aquastat Limit not working properly. I need help here.

I am currently out of town. I have shutoff all power to the Tekmar Control and the Boiler to prevent continuous circulation pump operation without hot water. (I have backup heat pump operation to keep the house warm to prevent pipe freezing while I am away.) But I need advice on restarting the cold boiler for domestic hot water (DHW) when I return on Sunday.

First Question: Can I turn on the Boiler to without causing any problem?

Second Question: Any other possible causes for the main burner shutting down (Limit not working, ...) and possible remedies?

Thanks

mattmia2

Does it stop while it is firing or does it fail to light in the first place? it is probably the burner safeties locking out but you need more information to know if it is because it is failing to light or because it is failing to detect if it lit. Using a meter when it is not firing will rule out the other safeties like the high limit and the rollout switches and the t-stat(in this case the tekmar).

JLFT

Good question. The Tekmar is set to prioritize DHW demand over boiler demand. I have not seen the main burner flame shutdown occur during DHW demand (Boiler Target 180 degrees). My question remains: Can I restart the system with only DHW Demand without harming the boiler as boiler water temperature increases from about 60 degrees to 170 degrees?

When the Boiler Demand pointer ON and Circulation Pump symbol ON the Boiler Target drops to 170 but the Boiler temperature cycles between 140 and 150 as the main burner fires and then shuts off. So more than likely main burner shutoff happens during Boiler Demand cycling. I don't know if it stops "while it is firing" or if "it fail[s] to light in the first place".

As I noted in my original post the "flame roll-out switch" is not the source of the shutdown since it is a “non-recycling switch” which requires replacement once it has been activated and I am therefore able to shutdown and restart the entire system normally. Likewise, I have jumpered the Tekmar Boiler Output terminals during burner shutdown without having the burner firing.

So when the burner is not firing, and there is a Boiler Demand from the Tekmar, where and how do I use the meter to assess the High Limit switch?

EBEBRATT-Ed

There should be a wiring diagram usually attached to one of the boiler panels

mattmia2

The way to test is to look for 0vac across t-t and the safeties and 24vac from common to piliot and to main on the gas valve.

You can jumper t-t on the boiler and see if it fires, that will tell you ig the problem is the boiler or the external controls.

Does the boiler itself have a separate t-t for heating and connection for a dhw call? A picture of the boiler controls could help f it is some sort of more complex control.