Lochinvar Boiler glitch

[Rainy City]

Hi there, I'm running into an odd problem with my boiler. By way of background, its a 2012 Lochinvar Knight WH110, running 3 loops with an outdoor reset. Heating only, and its been serviced anually and has been very reliable.

In the past year, once every 6-8 weeks during the heating season, the boiler will switch to "set point met" and the circulation pump will continue operating and the injection pump on boiler will stop. Normally it will then switch to "standby" and wait for the next call for heat. Once every 6-8 weeks however, the boiled will stay in "set point met" mode, while a new call for heat occurs and the boiler will remain that way for hours despite the system cooling down and not heating the house. Usually, when I discover this situation, I'll shut the system down, wait 5 minutes and it will restart good as new.

The service tech wasn't able to diagnose this last spring, largely because it didn't happen while he was here.

Does anyone have any ideas as to what might be causing this? Faulty outdoor reset perhaps?

Thanks

Eric

 

[Fitter30]

Boiler has met the water temperature set point, but is still receiving a call for heat from either a remote thermostat or a DHW thermostat."
Running outdoor reset ?

 

[Sponsor]

 

[Rainy City]

Boiler has met the water temperature set point, but is still receiving a call for heat from either a remote thermostat or a DHW thermostat."
Running outdoor reset ?

Thanks Fitter 30.

Correct. Boiler has met the set point, and then stays stuck in the "setpoint met" mode with the circulation pump running. It will stay that way for hours (or until I notice the house getting cold). I have no DHW, but one or more of the 3 thermostats will be calling for heat.

Yes, I'm running an outdoor reset.

Worth noting I'm in Victoria BC, so the outdoor temperature is seldom below zero (C). Im not sure if that is a factor.

 

[Fitter30]

Outdoor reset has a 70° f default temp. Need to compare outdoor sensor temp on boiler and compare it with outside on a sunny day. Sensor usually don't go bad getting a difference temp reading once every 6 to 8 weeks it happens a lot more than that. Od sensor position can be a pain for the right spot. Here's a service manual.

https://www.google.com/url?q=https://www.lochinvar.com/lit/898871100305187_2000558071_Rev%2520B_WHB%2520Service%2520Manual%2520(34309).pdf&sa=U&ved=2ahUKEwjdoq7un4T8AhVekYkEHdaDDxoQFnoECAoQAg&usg=AOvVaw1-2Uin_w9OAvrLf32K6Ym_

 

[Rainy City]

Thanks for this Fitter30. Much appreciated. I'll do some sleuthing.

 

[Fitter30]

Any change made write down old and new settings

 

[Rainy City]

Any change made write down old and new settings

Just to follow up, i think I found the problem.

Three weeks back I was looking at my boiler as it was stuck in the `set-point met` glitch. This meant that the circulation pump was running, the boiler was not firing and the temperature continued to drop. As I mentioned last time, the system pump was not running. I started scrolling through the data and noticed that it said that BOTH pumps were running. I decided to switch the system pump to medium speed (its a Grundfos and it normally runs at low) and suddenly the pump kicked in. Within a minute the boiler indicated that the outlet temperature had dropped and the boiler fired. Its been working perfectly ever since.

The only thing I can conclude is that the pump has a wiring problem that causes it to fail on the low speed setting. That intermittent failure allows the boiler to think its functioning normally and the pump blocks hot water between the boiler outlet and the pump which the boiler sensor interprets as meaning the water temperature is sufficiently high as to not require firing despite the call for heat from the thermostats. The short section of copper stayed quite hot when it was stuck in the `setpoint met` glitch.

Fingers crossed that this indeed the issue. If necessary, I can easily replace the pump. The system doesn't seem to perform any differently with the system pump on medium and the larger circulation pump on low. Pressure is normal.

Thanks again for the input and advice.