Worcester 28cdi intermittant fault

[dougal]

one difficult job, the boiler will work for hot water and heating for around 30mins, then boiler goes out followed by hot water light flashing rapidly. the manual says air flow fault, colleague has replaced air pressure switch, i ve checked all air tubes for splits and blockages, replaced fan still get the fault. checked both thermistors and resistance o.k for temp. rang worcester not very helpful said replace p.c.b luckily had one on van swapped it but made no difference, checked electrode and flame rectification gaps o.k. ckecked gas valve max and min o.k. flue is horizontal is on first floor. after couple mins boiler will come back on again on its own.

anyone else had this problem?

cheers:innocent:

 

[willing2learn]

Hi,

Have you tried changing the harnesses for all the electrodes? This can sometimes be the cause of the fault you describe.

 

[glenno1]

have you checked flue is clear and in 1 piece

 

[diamondgas]

Certainly sounds like an airflow issue --- Have you measured the APS venturi difference +/- ? Is the fault constant or intermittent? Condensation can cause the APS to lock open or slow to switch off when the fan stops...

I don't know what pressure diff you should be registering but it will be written on the APS ...

 

[dougal]

thanks guys for your inputs,couple things for me to look into. voltage is dropping out on fan, air pressure switch deactivates then hot water light flashes only thing running is pump, then after 2 mins boiler will come back on its own it is intermittant can stay on for 30mins before fault occurs. checked continunity across harness to fan and air pressure switch all o.k. flue is all o.k

thankyou guys

 

[diamondgas]

that something i didnt think of,

thankyou

Not knowing flue length or position in relation to corners, eaves etc, the Diff pressure to lift the APS is worth examining IMHO