DHW problems with Alpha 240e boiler

8 Aug 2006
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United Kingdom

My Alpha 240e is having problems with DHW at the moment - it has been going on for a month or so - I would be very grateful for any advice!

Basically, the boiler will not produce properly hot DHW unless the CH is on and the radiators have heated up. CH is absolutely fine. The boiler appears to be quite old and we haven't had a service yet as we are quite newly moved in.

The boiler seems to be supposed to produce about 9.5 l/min with 35degree rise; max DHW should be 62degrees. I have tested the flow rate with CH on and it does achieve this.

Cold water temp is 9degrees.

At present, set to 'DHW and CH' with the CH off I am barely getting hot water from the tap at 30degrees at 9.5 l/min.

Set to 'DHW only' I'm getting a maximum of 45degrees out of the tap on a very slow flow.

The neon lights on the front of the boiler seem to indicate that everything is functioning as it should according to the instructions, but the overheat thermostat light comes on for a split second when the burner lights and then turns off again - nothing about this in the instructions so don't know if normal? - this seems to only happen when calling for DHW when set to 'DHW and CH' but with CH off. Might be a bit of a red herring?

Thanks v much in advance for any help!
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At best the diaphragm has perished, at worst diverter valve is stuck. Very, very common on these.

Does the ch flow get hot when the hot tap is used on DHW only?
Thanks :)

Yes - some of the rads get warm when the DHW has been on for a while (after a shower for instance)
It sounds like the DV then. I always replace with new complete unit (expensive but I can offer a full warranty), whilst others on here prefer to buy the recon kit and strip it out (very cheap in comparison).

Depends on you, if you want to do it, which way to go ;)
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The moving parts in the rear section are sticking and not following the front part.

When you take DHW some of the heat goes into the rads.

You can restore full performance by closing the valve on the CH flow or return.

I have never been very successful in cleaning the rear parts so I would aim to replace for a customer too.

If it was my own I would boil in citric acid and then disassemble and boil the parts again and then wash and dry and then silicone grease the seals.

Doing all that is not commercially cost effective and a new unit is the best solution.

:eek: I use a scotchbrite pad and a penknife and haven't had any trouble! Lime-lite's ok for things you can't get into.
Hi - thanks for the advice on this one. The heating engineer has now been out and has confirmed that:

a) both the primary and diverter flow switches seem to be switching from visual inspection - (does this necessarily mean the Diverter Valve is actually working?)

b) the CH flow pipe under the boiler is hot when tap is calling for hot water in DHW mode

He reckons it's a blocked DHW heat exchanger and has put some chemicals in the CH system via a radiator - he told me to run the CH and turn the hot taps on intermittently. He doesn't hold out much hope for this working and reckons we need a new boiler (££££ eeeek!)

Is there any way of diagnosing whether it's the DV or the Heat Exchanger?
Can I do this by closing the CH flow or return valve as suggested by Agile ?
Get another heating engineer :eek:

A blocked plate HE will not cause the rads to get hot whilst the hot tap is on. This is defo the DV.

Usually cost around £250-£300 all in for a new one.

Can't see why he is suggesting a new boiler :eek:
Thanks for the super-quick response...

Yeah - I thought the diagnosis sounded a bit wierd but can't really get my head round how it all works so wanted to check. I guess worst case scenario is that it's both the DHW Heat Exchanger and the DV but we won't know that until we've had the DV fixed I suppose! - the boiler is a bit of an antique.

Now to find another heating engineer in Bristol.... (and to stop researching prices for new boilers!) :)
I think Chris Hutt who posts on here is Bristol way. Try finding his details on here.

He is good.

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