Worcester Bosch fires on, off, on off, - any ideas?

[shminkypinky]

Hi there. I have a 7 year old Worcester Bosch 28i RSF.
Occassionally when the heating is on I can hear the boiler fire up, extinguish then fire up and extinguish continually in a loop until it sorts itself out.
I can hear the relays in the control board turning on and off really fast.
Its as if the boiler thinks its a temperature then thinks 'no', I need to re-light, 'no' im up to temperature extinguish.
Can anyone shed any light on what might be wrong and point me in the direction of the part that needs replaing??

Just so you konw the boiler was doing this before christmas so I had it serviced but it is still doing it. Tonight when I turned the temp knob up on the front of the boiler it stopped its crazy loop, fired up and stayed fired up which is why I thought temp related.

Any advice would be greatfully recieved.

Thanks

 

[BARNY78BG]

most likely could be central heating sensor faulty

 

[shminkypinky]

would that be the temp sensor inside the boiler?

 

[BARNY78BG]

yes but it's best to get rgi to check it out as they will know how to check it to confirm resistances.

 

[shminkypinky]

Any ideas what a new sensor is likely to cost???

Also is it inside the burner or coupled to a water pipe inside the boiler?

Could it just be cleaned?

 

[nickb1984]

Possible pcb fault what you can hear is the relay clicking which is linked to pressure switch.
I had same problem on 24i rsf 3 weeks ago.
There was all carbon/arching marks on relay,changed pcb worked a treat

 

[Whitespirit66]

Just so you konw the boiler was doing this before christmas so I had it serviced but it is still doing it.

Did you mention the fault to the engineer?

 

[shminkypinky]

I did mention fault to engineer who suggested the service may sort it out. He did mention possible PCB replacement though as it sounded familiar with one they had just recently replaced.