Worcester heatslave oil boiler combi thermostat cut out

[villiers1041]

Hi all got a heatslave oil combi that no matter what I do will always go.out on the thermal reset .
I have
Change pump twice
Changed diverter valve twice
Changed control panel and all thermostats too
Pumps running
Pressures fine
Bled all boiler vents and radiators
Works fine for 15 minutes and then the trip happens
It is NOT the burner reset its the thermostat under panel
Many thanks

 

[Johntheo5]

It may be the boiler control stat has failed, the burner then keeps firing until tripping on the hi limit stat which doesn't operate until 110C to 113C, but you may also have changed this?
Is the pump a A rated pump?, if so make/model/mode/setting, most now display the power in watts and some also display the flowrate in m3/hr.

 

[villiers1041]

Changed control stat yes .
I will try again with a new stat
Not a rated at all

 

[Johntheo5]

Does it do the same while producing HW?

 

[villiers1041]

Yes
Not just heating but does same if only hit water is on.

 

[Johntheo5]

hi limit stat also renewed?, if you turn the control stat down during the 15 minute firing period, does the burner stop firing and resume when you turn it back up?. Cant think of much else.

 

[villiers1041]

I will look at those later thanks.
The manual says to put the reset stat then limit stat then control stat in same pocket.on boiler.
But on mine the control stat is on a separate pocket to the right above burner,still with a split pin in place

 

[villiers1041]

Well
Changed heat exchanger tonight just in case and nee diverter valve, still same .
Happens if just hot water is on or heating on.
If heating on the rads get hot no problem then the reset kicks in so think.pumps running ok .
Have had these boilers 15 years and built up a lot of spares so I can swap.parts easy but never had this before.
Auto air vent bled too

 

[Johntheo5]

Did you do the control stat test, if you keep turning it down does the burner cut out??,

 

[villiers1041]

The heating control you mean mate ?

 

[Johntheo5]

Yes, that should have a range of ~ 45C to 75C, if that doesn't trip the burner when turned down then clearly a control stat problem, if it does but the burner trips at setting of say 70C then a overtemp stat problem?

 

[villiers1041]

So
Heating stat turn on and off ok no problem and turns off burner fine.
Reset stat changed and exactly the same!!
What next the water stat?
But that seems fine
Very odd

 

[Johntheo5]

Its the boiler water stats I'm referring to at all times, and the control stat is the one that sets the boiler water temperature setpoint, is this the heating stat above that you say you turn off and on?, if not, fire the boiler on CH, with boilr control stat set to say 70C, after say 10 mins or so turn the setting down until the burner cuts out, it should then refire when the water temperature falls, is it doing this?

 

[villiers1041]

I will check.
In morning
Really appreciate all your help. Cheers

 

[villiers1041]

So
It worked fine for a while
All controls working as they shoukd and hot water and central heating fine , then I turned heating off last night and then checked this morning reset tripped again