Vokera 20/80RS flowmatic CH cutting off at 15 degrees

[owington]

Hi Everyone,
New member here after some help with a friends boiler. Basically the CH will fire up fine when the room thermostat is turned up but on reaching around 15 degrees will cut off and then constantly fire and cut off. The hot water runs fine. It is quite an old boiler and not one i have come accross in my short time as a gas fitter. Any ideas? Im thinking boiler thermostat is faulty? Thanks

 

[Puddle]

There was a design fault with this boiler,as there was no time delay on pcb and worked by immediate responce to boiler stat just turning on and off as you say,when it gets hot
They brought out a modification,which was basically just a time delay that fitted on the corner of the original pcb but not sure if they still supply it, as so old now,maybe a call to volkera to check

 

[owington]

Thanks for the reply mate. Is this something that is likely to crop 10 years after the boiler has been fitted or would it be evident from the start. I ask because the boiler was working fine until recently.