Baxi constantly firing up when no hot water demand.

stehodgy · Posted: Sun Feb 14, 2010 1:16 pm

I have a Baxi Combi 80Eco boiler. It is firing up every 10 seconds or so, stays in for a couple of seconds, goes out and then repeats. This happens when the control is set to DHW/CH and the heaters are warmed up and the hot water tap not turned on and it also happens when the control is set just to DHW alone without any taps being turned on at all. The only time it doesn't fire up is when the control is set to off. Any help would be appreciated.

stehodgy · Posted: Sun Feb 14, 2010 3:04 pm

A couple of days ago the diaphragm and pushrod were changed in the DHW pressure diff valve because there was a small leak coming from there, I think the boiler was drained to do this.

stehodgy · Posted: Sun Feb 14, 2010 3:44 pm

Elvispresley wrote:

If it has happened since the repair then there is no need for me to draw you a picture, is there really.

There might be a need to draw a picture as I'd like to sort it myself. Right, I've been to look at the job he did and looked not only at the DHW diff valve but the CH diff valve. Whichever position the control is in (except off) the pushrod in the CH valve makes the microswitch and doesn't go off even when the hot water is turned on, the only time it doesn't touch the microswitch in the CH valve is when the control is in the off position.

ChrisR · Posted: Sun Feb 14, 2010 3:51 pm

SOunds like he might have got water on the PCB. You could try gentle drying with a hair dryer.

Flame is recognised by a tiny current, which water would interfere with. Boiler thinks flame not lit, so it cuts gas to have another go.

There's NO pushrod for CH alone, that's for the pump, whioch operates whenevee the boiler's on.

stehodgy · Posted: Sun Feb 14, 2010 4:22 pm

ChrisR wrote:

SOunds like he might have got water on the PCB. You could try gentle drying with a hair dryer.

Flame is recognised by a tiny current, which water would interfere with. Boiler thinks flame not lit, so it cuts gas to have another go.

There's NO pushrod for CH alone, that's for the pump, whioch operates whenevee the boiler's on.

Thanks I'll give that a go. I probably should also say that when the heating is put on from cold the flame stays lit until the heaters are warm and then starts firing up every few seconds and doesn't stop. Altho it starts right at the begining when it's just the DHW on when no hot water is required.

gas112 · Posted: Sun Feb 14, 2010 7:28 pm

Faulty microswitch . The one the hot water pin activates

stehodgy · Posted: Sun Feb 14, 2010 9:14 pm

gas112 wrote:

Faulty microswitch . The one the hot water pin activates

Thanks, is that a job i can do myself possibly?

stehodgy · Posted: Mon Feb 15, 2010 6:46 pm

gas112 wrote:

Faulty microswitch . The one the hot water pin activates

Cheers, I changed it today and it's working properly again.

ArnoldJ · Posted: Wed Feb 24, 2010 8:01 pm

I have the same problem but alas I'm going to have to call out the plumber because this is way beyond my (poor!) DIY skills. So could someone confirm exactly what part I need to ask them to change? You mentioned microswitch......?

A plumber did come out to 'look' at the problem and said it might be the PCB and would go away and order one.... I never heard from him again!

Thanks.

weargas · Posted: Wed Feb 24, 2010 8:48 pm

dhw microswitch assy for the eco is what you ask for, it comes attached to a full wiring harness including connections to the pcb, selector switch, terminal strip and pump. You can do a shortcut by cutting the wires of the microswitch and just replacing the switch. I like to do it the proper way:)
Baxpoti will supply you with a part number as it's not on any of the exploded diagrams in spares suppliers for some reason.

ArnoldJ · Posted: Thu Feb 25, 2010 9:46 pm

weargas wrote:

dhw microswitch assy for the eco is what you ask for, it comes attached to a full wiring harness including connections to the pcb, selector switch, terminal strip and pump. You can do a shortcut by cutting the wires of the microswitch and just replacing the switch. I like to do it the proper way:)
Baxpoti will supply you with a part number as it's not on any of the exploded diagrams in spares suppliers for some reason.

Many thanks for such a quick response! I now feel more confident in what I need to ask for. Much appreciated....

Agile · Posted: Fri Feb 26, 2010 2:02 am

ArnoldJ wrote:

A plumber did come out to 'look' at the problem and said it might be the PCB and would go away and order one.... I never heard from him again!

Thanks.

Thats typical of someone who does not really know whats wrong!

Changing the switch and wiring assembly is rather stretching a DIYers capability as its quite involved.

I cannot advise it but I have seen some people who very simply cut the wires to the switch and just connect the three wires together using a choc block.

Tony