Central Heating not refiring on Vokera boiler

[brakes]

When I put on CH+HW the boiler fires up, reaches its temperature and cuts out and then only sometimes fires up again when the temp falls.

It will fire up again and stay lit for a while if I turn a hot tap on, but again it fails to relight when the temp has fallen back. I'm up and down at the moment turning a hot tap on to get it to refire.

Any idea on what the fault is likeliest to be?
Thanks.

 

[Terrywookfit]

It would be helpfull to know the model of the boiler to avoid wild guesses !!!

 

[brakes]

It's a Vokera Linea 7.

Thanks.

 

[nickso]

thermistor would be a good guess, but only a guess. the lineas are quite good at realising the thermistors are way out of calibration.

 

[brakes]

thanks. would that need an engineer to test?

 

[nickso]

simply because its a guess i would recommend you get someone to have a look. some faults become very obvious when you are standing in front of the boiler in question.

 

[MANDATE]

The symtoms described fit a faulty 3port mid position valve. That is if you have one in your system.

 

[nickso]

its a combi

 

[brakes]

A reply on another thread talking about a similar fault suggests a faulty diverter. Could this be the case here?

 

[bengasman]

When I put on CH+HW the boiler fires up

how do you do that on a combi?

 

[Agile]

A reply on another thread talking about a similar fault suggests a faulty diverter. Could this be the case here?

No !

He gets CH + HW by running the Ch and then turning on a hot tap!

Of course thats not really both at the same time, just one followed by another!

On most boilers that problem is a faulty PCB . I suspect its a faulty anti cycle timing circuit but as yet have not had time to investigate that.

Tony

 

[brakes]

Agile, yes, thanks, that is what I meant.

Re possible PCB fault, wouldn't the fault be total rather than intermittent if the board was at fault?

I suppose the board would be expensive to replace. Are there commoner, less expensive faults that I can rule in or out first? Thanks.

Finally, Servo serviced it last time and replaced the diverter valve since the rads were heating up on HW when a tap such a the shower was being used. The charge for the service and valve was rather high for what seemed a very quick job. Any recommendations as to who might do a good job in NW London for a bit less?