Worcester Bosch 28CDi RSF Combi problem

Hello, A couple of weeks ago I got suspicious that a small amount of water may have leaked from the bottom of the boiler onto the surface below. I put a "collector" thre to get an idea of the amount. I checked it a few days ago and there just seemed to be a small patch ((worrying in itself).
Today, I had trouble with the how water demand - turning a tap fully on would activate the hot water from the boiler, but lower flows, eg my morning shower, would not get it to heat up.
Since then, I have noticed that larger amounts of clear water have leaked from the boiler into the tray, eg perhaps enough to fill a mug by 1 cm every half hour.
Does anyone have any experience of this or ideas on what might be wrong?
Also, I have tried contacting Bosch as I seem to recall they used to offer servicing and repairs directly, but I am having trouble finding contact details.
Do Bosch still offer direct repairs and servicing, or are there any other reliable specialist firms who I could contact, rather than plucking an outfit at random from the yellow pages? My location is West London.
Thanks, Richard Hamer
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Their web site is http://www.worcester-bosch.co.uk / You can contact them for service/repair or with a technical query via the web site, I found them very responsive and helpful.
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richard snipped-for-privacy@yahoo.co.uk writes

How strange! My Worcester 28Cdi RSF had similar problems a few weeks back too...
I had excessive changes in pressure, lack of hot water and water appearing from the pressure relief valve.
Check Ed Siretts FAQ - it will answer everything!
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
What's the system pressure doing? If it's peaking at 3 bar then the relief valve is opening - hence the water leaking? If so your pressure vessel may be ruptured. Check the air valve on it. If water comes out, you'll need a new vessel. The easy way to replace it is to take the boiler off the wall, drill out the rivets that hold the mounting plate and drop it out of the back.
Lack of hot ware could be the diverter valve. Take the flow switches off, by removing the C clip and take a look at the plunger pin. It should come out when the hot tap goes on. If not, you need a new valve.
We used an Ariston (i think) diaphragm instead of buying a whole new valve.
The install manual is available on the net, it has a fault finding chart which may help.
God, I didn't even know what a combi boiler was last month.....!
TTFN
--
Richard Markham

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Worester Bosch were very good. responded to my email within half an hour (I was most surprised - I usually despair when I have to rely on organisations replying to emails, particularly urgent ones ...).
I managed to book a next day "tiered price" appointment - ie one price if it just needs service, another if it needs any parts, and a third price if the heat exchanger needs replacing. Not unreasonable, particularly when it's being serviced by trained Bosch people, and nice to know the cost is capped.
He sorted out a long standing problem which I posted about a few years back - when the central heating temperature dial is close to the actual temperature, for low settings, the boiler repeatedly fires up then shuts down instantly, over and over again. For the benefit of anyone else who has this problem, he replaced the main controller board.
He also replaced the heat exchanger plate, which was the source of the leak.
However, in terms of hot water not firing up, he said the boiler seemed fine and that he thought the problem was cross-flow in a mixer valve, presumably high pressure cold water leaking through a mixer into the hot water inlet.
Now, I know that my shower does have this problem, but am not sure why the boiler is suddenyl unable to cope with it after five years. Alternatively, it could be a new mixer fault elsewhere.
Does anyone have any ideas on how to easily diagnose the source of such a mixer problem - I have four sets of mixers - without physically disconnecting each pair of taps in turn and trying the hot water until it works?
Would I be right in thinking that the more modern taps, such as a 4-year-old kitchen tap, which have physically separate outlets for the hot and cold streams in the tap head, cannot be the source of such problems?
Hope all this helps someone in the future ... Thanks, Richard
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Having isolated put a stop end in the hot water pipe out of the boiler, so that only a single (washing machine) outlet is in the run, the hot water problem remains.
The tap needs to be turned fully on to get the boiler to fire up. This is a much greater flow than used to be necessary for hot water, and the kitchen sink and shower are unable to trigger it.
I am therefore sure the problem is within the boiler itself. All other problems have been fixed. Bosch will be back in a week to take another look, but in the meantime does anyone have any ideas on where the problem might lie, eg the hot water diverter valve / flow switch sensor thingy?
Thanks, Richard
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On Sat, 21 Feb 2004 05:06:15 +0000, Richard Hamer wrote:

The web site is down ATM so I can't check the precise means by which the boiler senses water flow. However the symptom of insensitivity to HW flow is very likely to indicate a split diaphragm of some sort. This part will likely not exceed 40 (whole valve) or 10 a replacement diaphragm.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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Valves are 75 plus vat and you can't get the diaphragm as a spare part!
--
Richard Markham

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writes

Take a look at the B E S Website and see if your valve is among those they sell. Most of the Worcester valves are made by Giannoni which is what BES sell
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