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Andrew Smith
Andrew Smith, Home Appliance Technician
Category: Appliance
Satisfied Customers: 3757
Experience:  Gas cooker specialist
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Intermittently my Baxi Solo 2 PF gas boiler & pump continues

Resolved Question:

Hi. Intermittently my Baxi Solo 2 PF gas boiler & pump continues to run after the programmer has switched both CH & HW circuits off. Normally the boiler should switch off and the pump run for 8 mins to cool the system down. The only way to shut it down is by manually turning off the mains supply. As a precaution the boiler PCB & HW thermostat were replaced in early Dec but the problem re-occured yesterday. Advice on what to check/replace next would be appreciated.
Submitted: 2 years ago.
Category: Appliance
Expert:  Andrew Smith replied 2 years ago.
Your boiler is turned on by the motorised valve.Try turning off the water and heating and checking the lever on the motorised valve and tell me if it slack or tight?
Customer: replied 2 years ago.
With CH & HW off the lever on the motorised valve is tight. This valve was new in Aug 2012. With the CH & HW on the lever moves according to the demand from either tank or room thermostat.
Expert:  Andrew Smith replied 2 years ago.
Ok - good.
When the boiler is running on, are you able to check for power at the SL connection on the boiler?
Customer: replied 2 years ago.
I'm now away for New Year but did check yesterday that with boiler running there was power at the SL terminal.
Expert:  Andrew Smith replied 2 years ago.
Ok, we just need to check for power ther when the boiler should be off, try to narrow it down if it is a boiler fault or a control issue.Come back to me when you are in front of it again.
Customer: replied 2 years ago.
I regret not getting back to you but I've been diverted by family matters. After the programmer has switched the boiler off there is power at the SL terminal - about 40v.
Expert:  Andrew Smith replied 2 years ago.
Ok, sounds like a motorised valve fault.Try disconnecting the grey and orange wires and seeing how it behaves?
Customer: replied 2 years ago.
Before I started the system had previously shut down with the motorised valve lever against W (for Hot Water). With power off I disconnected Grey & Orange wires - then power on and Programmer on for CH & HW the lever moved to the M (mid-position).
Note: - before submitting the query I had checked that the motorised valve responded correctly to both the tank and room thermostat settings.
Expert:  Andrew Smith replied 2 years ago.
Does the boiler shut down correctly and not overrun with them disconnected
Customer: replied 2 years ago.
Having disconnected both wires:
a) Turning the power on and Programmer on for CH - the boiler does not fire up even if the room thermostat turned up.
b) Additionally setting the Programmer on for HW - the boiler fires up and the motorised valve lever moves to mid-position. After a while the boiler shut down and the pump completed its normal 8 min overrun cycle. Turning the tank thermostat up caused the boiler to fire up again and subsequently shut down normally.