Glowworm Ultimate 120 ff boiler pulses when powered up

[haggers]

Hello there, can anyone help?
My boiler works fine when CH or HW, or both are selected, but as soon as they are both switched off via the timer, the boiler hunts, fan switching on and off again every couple of seconds continually, and therefore the boiler does not fire up.
I have replaced the fan and pcb. the first two leds are on and the troubleshooting chart suggests the air pressure switch should be replaced (power gets to the switch, but the 'C' connection pulses. I have checked the air tubes for blockages (both are ok) and I know the fan is ok. If I disconnect one tube from the switch, the fan runs ok. So is it the air pressure switch which is at fault?
Regards, David

 

[45yearsagasman]

You seem to be eliminating faults by chucking parts at the boiler so why not carry on. To advise you that this work should only be undertaken by a competent person is a waste of time, so I won't bother. I don't think you will get any DIY advice.

 

[haggers]

The fan and pcb replacements were to fix previous problems, not the one I have now.
Any advice would be still be appreciated.

 

[Agile]

Changing a fan should be done by a gas reg engineer and not a DIYer.

Tony