Did dead mouse cause boiler to turn on?

[Sprinkler]

We have a Domusa MCF - DXV sealed room boiler, and yesterday on returning to the house, found that the boiler had turned itself on, rads were hot and DHW also hot. And the pressure was at almost 4 bars.
First, I turned off the boiler on/ off switch, but it stayed on anyway, so had to disconnect the power supply cables. I also saw burn stain on the plastic connector, (which I intend to replace) where neutral and ground power supply wires are connected.
Finally, I discovered a dead mouse stuck to the power supply board. I then cleaned off the power supply board (see photo), reconnected the boiler, but had the same problem of boiler staying on. Do you think a new power supply board might solve this problem? Thanks

 

[Sylvan]

Yes

 

[Sponsor]

 

[Sprinkler]

Ok, thanks

 

[Dana]

As long as the fried board didn't apply excessive voltage or current to other control components replacing it will probably work. For sure the system won't work properly without replacing the board.

There is a very remote chance that cleaning off the board with isopropanol and letting it dry could make it work, but I doubt it. It's hard to tell from the picture how much of the crispy stuff is burnt electronic components vs. burnt mouse bits. Fried mouse-carbon can be fairly conductive creating short circuits on the board. But the board is probably toast.

 

[Sprinkler]

ok, I hope to collect the new board and 3 pole plastic connector next week. But before replacing the board, I want to look into getting any other mice out of the boiler. Any ideas how to remove mice? I suspect there may be a nest in there in the middle of the insulation. And also to actually try to seal with fine wire mesh, the openings at the back of the boiler where pipes and cables enter. And then have a close look around the garage and basement to seal any possible entry points. And lastly replace the power supply board and connector. I did try cleaning the old board with cleaning alcohol and a new toothbrush, but it made no difference.Thanks!

 

[Dana]

In Istanbul many people feed and pamper the feral cats to keep the mouse population down, but I don't think you want to put a cat in the boiler.

 

[Sprinkler]

Hi, I finally got round to fitting a new power supply board on the oil boiler, but unfortunately when I turn it on, the burner starts but neither the radiators nor the water get hot. The burner switches off at the max temperature ( 80 or 85°C) and then the temperature continues to rise to around 95°C, then goes down slowly. I suppose the burner would come on again when the temperature falls to 80° - 85° but it takes ages. I think I fitted the new board correctly. Any ideas what the problem might be? Thanks

 

[Dana]

It sounds like the boiler's burner controls are working fine, but whatever is controlling the pump isn't, or perhaps the pump is defective (which could be tested independently.)

 

[Sprinkler]

Yes, I also suspect the domestic hot water circulation pump. I was thinking of using a phase tester screwdriver to see if current is reaching the pump after the I turn the boiler on. I also wonder whether there might be a blown fuse in the plastic box attached to the pump? At least I assume there's a fuse there? Or how would you suggest testing the pump? Using a screwdriver, I found that it seems to rotate freely. Thanks.

 

[Dana]

If you have some electrician skills, disconnecting the pump wiring from the system controls, then temporarily wiring it to a switch on a cord that plugs into the wall would allow you to test if the motor turns when the power is applied. (If you don't know how to do that safely, don't try it.)

 

[Sprinkler]

If you have some electrician skills, disconnecting the pump wiring from the system controls, then temporarily wiring it to a switch on a cord that plugs into the wall would allow you to test if the motor turns when the power is applied. (If you don't know how to do that safely, don't try it.)

Ok, that sounds like a good idea. I agree with you about working safely - it's so important to be very careful while doing any electrical work. So, hope to report back tomorrow with the result. Thanks!

 

[Sprinkler]

Good news! First I decided to open the plastic cover attached to the pump, just in case I might be able to find a blown fuse, but everything looked normal. Then I did as you suggested - disconnected the pump from the power supply board, and connected it to a wall socket, and it seemed to be working ok - I could hear a low hum, etc.
Then, after reconnecting the pump to the power supply board and turning on the boiler, I used a phase tester screwdriver and saw that power was reaching the pump cable connector. Also, the sensor cables came unplugged accidently, so showing error 51 (or S1?) on the boiler display. Anyway, after reconnecting the sensor cables, the error message went away. I also opened the cap on the automatic (?) Bleed nipple above the pump, leaving it loose. Then I left the boiler on and it worked correctly! The water got hot! And I'm not sure what the fault was. Unless, maybe disconnecting and reconnecting the pump to the power board resulted in a better connection to the pump.
Anyway, thanks for the very helpful advice!