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[ALDA]

Hi all you electrcal guys,

PREVIOUS POST SUBJECT,

What fault (ELECTRICAL)(MECHANICAL)(BOTH) would cause a combi boiler to start operating without a demand?
Could it be electrical/electronic?
The boiler is a Worcester Bosch combi 240 rsf.
This fault only "occasionally" happens.
The combi does not have a frost thermostat fitted.
Once the boiler operates, it cannot be stopped by switching the combi advance switch or by turning the room thermostat off.
The boiler can only be shut down at the mains switch.
The boiler appears to be firing up in the DHW mode, as the burner pressure is greater.
Also, because there isn’t an HW tap open, the radiators are heating up fast until the system shuts down after about 3-5 minutes.
The fault will occur once and then boiler goes back to normal operation.
Any replies will be gratefully received.

ALDA.

[ericmark]

I looked at your boiler on the worcester-bosch and I could only find operating instructions. I don't know your boiler so I can only talk in general terms. Many boilers have a timer to run the pump for a few mins to stop them sizing up if not used for a long time. Also some have a small tank of hot water to reduce the delay when you turn on the taps. This will be reheated every so often. As a result the firing of the boiler may be correct just the length of time it fires for being wrong. I would guess on a fault on the main board will have changed this time. You can try ringing worcester-bosch they may help but often they require a Corgi registration number before they will release technical information. But they should be able to tell you who can repair it in your area. Most electronic boards use "Micro-Chips" which are programmed and without very special equipment to read them, one has no idea what is inside, and the part number does not mean a thing, so it is in the main impossible to repair boards and new ones often require a Corgi number to be able to buy so DIY repair is impossible.

[ALDA]

Thanks for those thoughts on the matter Ericmark.

Could you tell me wether the micro switches activated by the diverter valve actuating rod have to be switched before any other electrical/electronic circuits can function?

What would be likely sequence of electrical operation of boiler?

I value your opinion.

Thankyou for taking the time to help, it is much appreciated.

Cheers,

ALDA.

[ericmark]

Sorry can't help non of the combi boilers I have wired have gone wrong. All diagnostic work has been on older units. With the newer boilers if things do go wrong it is normally done by manufactures trained service guys rather than electrician or plumber as one invariably need to fit a spare card etc. to test if it is that at fault and only the manufactures own guys are likely to carry those spares.

[ericmark]

Sorry can't help non of the combi boilers I have wired have gone wrong. All diagnostic work has been on older units. With the newer boilers if things do go wrong it is normally done by manufactures trained service guys rather than electrician or plumber as one invariably need to fit a spare card etc. to test if it is that at fault and only the manufactures own guys are likely to carry those spares.

[ALDA]

E,

NO BOTHER,

THANKS FOR YOUR IMPUT.

CHEERS,

ALDA.