Boiler Overheat

[dave2]

I have a wall mounted Baxi Solo 2 80 PF which started overheating.
I have had changed the fan and thermostat sensor, but it still overheats.
Any suggestions as to cause?
I have bought an oveheat thermostat kit and that is the next to be changed, but the one in my boiler is screw in, but the kit is a clip on type, which I am told is the replacement part. Anyone confirm if this is correct?

 

[ollski]

yes

is your pump ok?

 

[dave2]

Yes, no problem with pump

 

[ollski]

do your radiators feel any hotter than normal to the touch?....does it still cut out on the overheat when you turn the boiler stat down to minimum?

 

[ollski]

also this boiler has an 8 minute pump overrun to dissipate the heat. What sort of system are you running?, s or y plan?, trvs?, bypass with open valve?

 

[dave2]

The fan, thermostat sensor and oveheat thermostat have all now been changed.
The system ran for 9 hours without overheating, with the boiler thermostat setting set at just below 4 on the regulator. After tunring up to 4, within an hour, the overheat light was showing and the boiler shut down.
Regarding the rad temperatures, yes, they probably did feel a bit warmer than normal.

 

[ollski]

Ok lets start from the beginning, taking into account we can discount the boiler stat and the overheat stat. Does the pump continue to run for 8 minutes after the end of a central heating demand?, is the pump spinning at the correct speed?, have you visually checked the impellor is spinning?. What type of system are you on s plan or y plan?, is there a bypass?....is it open?

 

[dave2]

Sorry for my ignorance, but are what are the s and y plans?

 

[dave2]

Regarding the pump, this was renewed about 12 months ago.

 

[kevplumb]

Sorry for my ignorance, but are what are the s and y plans?

see this

 

[dave2]

The system is pumped heating and gravity hot water.
The pump does run on for a few minutes, but I have noticed that the pump is not on maximum, so I have now turned to maximum in case this would help, but everything has been OK up until now.

 

[bripl]

you have identified your problem with the information supplied now get a competent engineer to rectify the mistake,here are the clues
gravity hot water
pump runs on
boiler is not compatible with this sys as it has a built in pump overrun!!!
the water will not gravitate to dissipate the heat so goes to lockout

 

[dave2]

Sorry, my mistake in stating gravity hot water.
The system has run OK for 6 years and was installed and has been service twice a year by CORGI engineer.
It is he that has renewed the components mentioned above, although did state it was not the fan, but I asked for a change, whilst work was being carried out.

 

[ollski]

Ok so is it an s or a y plan? and does it have a bypass which is open enough to let the pump overrun dissipate the heat?. It may be an automatic bypass valve or it may simply be a gate valve.

 

[kevplumb]

ssss a white thing on the wall