Overheating Baxi Solo 2 R2

[sitethreads]

Hello DIYNot,

I'm facing a heating issue since replacing three radiators on the ground floor of my house. Our boiler now frequently overheats and I have to keep resetting the boiler to get it going again. Previously, we could leave the boiler running all day and it would start up the following morning without any problems. However, now it seems to overheat either after the scheduled heating period ends or when we manually turn off the thermostat. This results in no hot water the next morning, as we usually have the heating on in the evening.

The size of the three new radiators is the same as the old ones, but one of them was changed from a double panel to a single panel. Our system is a F&E S Plan.

Additionally, I've observed that the towel radiators upstairs require constant bleeding.

About a few weeks before the radiator change, I installed a Tado smart thermostat (but not the smart TRV valves). I believe this issue is unrelated to the thermostat, as everything was functioning well until we changed the radiators.

Our central heating pump is a three-speed Grundfos, which has always been set to the highest speed. I attempted to lower it to the medium setting about a year ago, but some radiators didn't heat up properly. In total, we have 12 radiators, including the towel rails.

The exhaust pipe leading back to the tank in the loft is slightly wet. I suspect this might be where water is escaping from the system, which would make sense if it's overheating.

Any insights or advice would be greatly appreciated. I will check this evening if the pump continues to run for a bit after the schedule ends.

 

[cross thread]

Check your boiler is shutting off after its call for heat has stopped,could be zone valve is sticking on.

 

[sitethreads]

The room hit temp quicker than I thought, so I wasn’t in the garage to check what was going on with the boiler or pump. When I went out the boiler had triggered the overheat switch though.

I reset, relit the pilot light and called for heat. Everything fired up, I cancelled the call for heat on the app and the boiler shut off as expected. I can hear a valve close and the pump ran for maybe 30secs. Obviously wasn’t hot enough because the pilot light remained lit.

 

[Agile]

I seem to remember that this boiler has a built in pump over run to cool it down after it has fired.

However for this to work properly the permanent live needs to be connected .

Many installers do not correctly wire up the boiler thus preventing the pump over run from working.

 

[ianmcd]

The room hit temp quicker than I thought, so I wasn’t in the garage to check what was going on with the boiler or pump. When I went out the boiler had triggered the overheat switch though.

I reset, relit the pilot light and called for heat. Everything fired up, I cancelled the call for heat on the app and the boiler shut off as expected. I can hear a valve close and the pump ran for maybe 30secs. Obviously wasn’t hot enough because the pilot light remained lit.

check that the bypass is open

 

[sitethreads]

I seem to remember that this boiler has a built in pump over run to cool it down after it has fired.

However for this to work properly the permanent live needs to be connected .

Many installers do not correctly wire up the boiler thus preventing the pump over run from working.

This could be it. Manual says pump overrun should be for 8mins.. I’ll investigate the wiring next

 

[sitethreads]

Ok, so I re-read the manual, and it's a 3 minute overrun, not 8. I just timed the pump overrun, and it was precisely 3 minutes. So it's not that!

I think I heard the valve shut off quickly yesterday and assumed it was the pump or I didn't leave the system on long enough.

I just bled some air out of 4 rads, which is a daily occurrence. I am running out of ideas now. I'll check the pump after the boiler shuts down to double check it isn't that.

 

[ianmcd]

AGAIN DID YOU CLOSE THE BY-PASS MISTAKENLY WHEN DRAINING

 

[sitethreads]

AGAIN DID YOU CLOSE THE BY-PASS MISTAKENLY WHEN DRAINING

Sorry overlooked your message. I’ve looked, but I can’t see anything that I could have mistakenly turned off. Some photos attached.

Where I drained off:

 

[ianmcd]

OK on your final pic, below the pump and slightly to the right that gate valve is your by-pass valve, with the boiler hot turn off both CH & HW and feeel that pipe is it staying hot ? it should that is how the pump over run facility dissipated the residual heat from the boiler when both zone valves close

 

[sitethreads]

OK on your final pic, below the pump and slightly to the right that gate valve is your by-pass valve, with the boiler hot turn off both CH & HW and feeel that pipe is it staying hot ? it should that is how the pump over run facility dissipated the residual heat from the boiler when both zone valves close

I was only running CH after seeing your message and shutting it down.

I’ve just felt that pipe after switching off CH and its cold. Pump runs for 3 mins after shutting down CH and I can hear the valve close, so where the hell is the water going? To me it felt like water still going through the CH, but it’s obviously hot and the vibration might just be the motor.

I’ve never touched either of those valves, how do they open? Surely if it’s open it should stay open.

Thankyou, might be getting somewhere.

 

[ianmcd]

I’ve just felt that pipe after switching off CH and its cold. Pump runs for 3 mins after shutting down CH and I can hear the valve close

well it should be hot, you turn the valve anti-clockwise to open, use a small adjustable spanner and turn it clockwise all the way in then turn it , back out again, they sometimes snap inside and need replaced, you eill know as you do it if it feels like it is actually closing and opening

 

[sitethreads]

well it should be hot, you turn the valve anti-clockwise to open, use a small adjustable spanner and turn it clockwise all the way in then turn it , back out again, they sometimes snap inside and need replaced, you eill know as you do it if it feels like it is actually closing and opening

I was able to give it a turn, and the pipe became hot. There was definitely nothing running through it before then.

How it became closed after changing some radiators is a mystery, there's no way I've forgotten putting an adjustable spanner to that. Hopefully, that's sorted the issue; thanks again.

 

[ianmcd]

I was able to give it a turn, and the pipe became hot. There was definitely nothing running through it before then.

How it became closed after changing some radiators is a mystery, there's no way I've forgotten putting an adjustable spanner to that. Hopefully, that's sorted the issue; thanks again.

yes that is definately your issue

 

[gas112]

I was able to give it a turn, and the pipe became hot. There was definitely nothing running through it before then.

How it became closed after changing some radiators is a mystery, there's no way I've forgotten putting an adjustable spanner to that. Hopefully, that's sorted the issue; thanks again.

as they are just cracked open a bit of debri could have moved into just the wrong position when you drained down to stop anything flowing through it