Worcester Bosch 28i Junior: hot water but no central heating

willpatrons · 12 Apr 2011

I have a Worcester Bosch 28i Junior combi boiler that I believe is about 5 years old (it came with the house we bought last year).

It has always worked fine, but suddenly the central heating has stopped working. When there is a demand for central heating, the boiler fires up and the indicator light comes on to show that the burner is lit, but this only lasts a few seconds and the light goes off. The boiler continues to make a humming sound (the pump?) and no hot water is reaching the radiators.

The system pressure is fine (just above 1 bar) and the hot water continues to work on demand - e.g. no problems taking a shower.

I admit to knowing nothing about boilers, but I wondered if it might be something simple that I could do myself - especially as the hot water is working fine. Or should I just call someone out to take a look? I fear that may be quite expensive though.

Any advice would be very gratefully received! Many thanks.

Agile · 12 Apr 2011

It seems to be a rather unusual fault and not something for which an immediate cause springs to mind. Of course in front of the boiler the cause might be very obvious.

The immediate question is have you had the boiler properly serviced each year?

Perhaps others might have encountered EXACTLY this situation and remember the fix but it is unusual.

You may need to get an engineer but it should not be particularly expensive. I would expect it would be little more than £100 if I was doing it. Worcester do fixed price repairs at about £215 which sets the maximum but is expensive if its something simple ( as I expect ).

Tony

willpatrons · 12 Apr 2011

Agile,

Thanks for the quick response.

As we bought the house and boiler last year, I do not know its service history. I would not expect it to have been serviced regularly though. Are you saying this is a must for the future?

I will look into finding a local engineer to take a look.

Thanks again.

boilerdoktor · 12 Apr 2011

had similar a few weeks ago...heating came on for about a minute there was a tapping sound like someone tapping a copper pipe with a screwdriver.

Turned out the heat exch and flow pipe was completely blocked with crud!

Is your hot water as hot as it was/should be?

Agile · 12 Apr 2011

That sounds completely different to what the OP has described.

Its also difficult to imagine a blockage seriously affecting the heating that does not have any discernable effect on the hot water where the greater heat output is more critical.

Tony

entreri911 · 13 Apr 2011

could be the divertor motor stuck, had a few of the earlier motors on them need replacing

Agile · 13 Apr 2011

Thats a possibility but with the boiler cold it would take several seconds to heat up and turn off, perhaps 15-25 seconds.

Then it would cycle every 15-20 minutes to keep itself warm.

Perhaps the OP could investigate more thoroughly and report back.

Tony

willpatrons · 13 Apr 2011

Thanks all.

boilerdoktor: no tapping sound, and the hot water temperature is unchanged from when the central heating was working.

Agile: when there is a demand for heating, the boiler fires up but then goes off after about 5-10 secs. The pump is working after that, as the boilers hums and I can hear water flowing in the pipe that supplies the upstairs radiators (altough this water is obviously cold). It does not seem to cycle every 15-20 minutes - it does nothing except have the pump running.

The other thing that I have just noticed is a electronic-type sound, similar to that from an old dot matrix printer, just before the boiler fires up for CH or DHW. This is like the noise the boiler makes after the reset button is pressed. I'm pretty sure it didn't do that when both CH and DHW were fine.

Thanks again for all suggestions. I'm getting someone in to take a look, and will report back what they find.

willpatrons · 14 Apr 2011

Problem now sorted. Diverter valve was stuck in DHW position. Had a new diverter valve motor fitted today, and both DHW and CH are working fine. Total cost: £128.

jackecole · 14 Apr 2011

I've heard of a few of these faults before. I find the best way to fault find this is by opening a hot tap and seeing if the combi still fires instead of going out so soon.

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Worcester Bosch 28i Junior: hot water but no central heating

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