Gloworm pcb 900847 on Ultimate boiler - indication leds

27 May 2012
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United Kingdom
Hi all

Gloworm Ultimate pcb 900847

Pilot flame on boiler won't light.

I have checked the two fuses on the pcb - both ok.

When 240V switched on the two leds on pcb flash momentarily then go out and a relay on the pcb picks up. Relay stays in until 240V switched off.

Question is shouldn't the leds stay lit? If so does this mean pcb is faulty?

ta very much.

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Check the pilot solenoid valve on the boiler.
Also check for good continuity on the ht lead
Thanks for the info Groovejet.

is the solenoid valve the item with the black lead/4 pin square plug on the end which is integral to the main gas v/v? Does it have two coils one for open & other for close? see attached photo

also since i posted......
1) I have managed to fire the boiler up via the HW request on controller and tank stat and with the radiator room stat calling for heat - the boiler runs.

2) HW request off and radiator room stat requesting boiler shuts down.

3) HW request & tank stat on their own the boiler fires.

4) also the 3 way v/v is making a right racket. seems much noisier than what I have ever noticed previously.

5) I'm having a look at the radiator room stat, its one of those programmable ones. will also look at 3 way v/v.

do you think I'm heading in the right direction.

thanks again.

room stat is working ok.

looking for wiring diagram for system to see where signal for boiler fire for CH is being lost.

anyone got any ideas?

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boiler now works ok for HW but still wont fire for CH.

I swapped the output functions of the controller so that HW & CH were crossed (ie on the wrong channel outputs) so that I could prove the controller. CH buttoin caused the HW to fire up so that channel looks ok, however the HW button would not fire the CH, so the fault moved.

3 way v/v is now quiet.

currently left like this - all wiring returned to normal, and CH & HW clocks set to the same therfore can have heat at expense of unnecessary HW. suspect I need to try and draw the schematic diagram........

Fault appears to be between the controller & boiler on the CH leg of the control circuit. Has anyone any ideas what it could be? I don't want to call in BG and I'm wary of a local man because of the nature of the fault as I can do electrical.

Groovejet suggested I check the pilot solenoid, but if the boiler fires for HW doesn't this mean it is ok? Or does it get seperate feeds from HW & CH controlls?

most likely problem, using your "fault description", is 3 port valve not working. What make is it?
Hello twgas

It's a Siemens MA322C

I have had trouble with this before. House builder snapped one of the fixing clips, didn't tell me & I didn't find this for ages so I have had it fastened up with tie-wraps.

I changed the synch motor last year.

Valve was making a right din this morning and one of tie-wraps had come off so the head wasn't seated correctly. I didn't connect the two......

I have replaced the tie-wraps -hasn't fixed it so will look at testing the v/v wiring tomorrow.

Have you any tips?

Thanks for the info.
If I do the tests and it is indeed the 3 way v/v actuator micro switch that is faulty how can I jimmy the HW & CH so that I can have the heating without scalding the rest of the family due to high temp on the HW. need to keep turning the tank stat up to get the CH on.....or am I missing a trick?

Just wanted to thank twgas & Groovejet.

I changed the valve as it was the Micro switch.

And for info the neons(thought they were LEDs) flash momentarily for power up and continuous for boiler firing.

Thanks for the help.


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