Combo dhw problem

3 Feb 2013
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United Kingdom
Sorry if this has been asked before I have read a few responses to similar questions but I want to ask.

I have a combi alpha cd25c, I don't the history of as it was installed before I moved here. After noticing on of the downstairs radiators was completely cold except at the top (it is top fed) I took off the radiator flushed out all the black sludge and reattached as refilled adding some sludge cleaner. I left this in for a week then drained down the system. I took the opportunity to replace a seized stopcock whilst I was at it. I added some boiler silencer refilled system. Everything is working, except te DHW doesn't seem as hot as you have to do the old trick I letting it run slow.

I understand it could be sludge in the secondary heat exchanger?
I was wondering if it is just increased flow after changing stopcock but in kitchen tap it is noticeably cooler but not terrible, I am concerned as I am soon to be running a thermo mixer shower off the boiler and need it at its best for that.
I dot currently have a boiler cover policy , should I take one out (would it be covered) or call a local heating engineer? Does it need powerflushing? Could I do anything myself ? I have caused it?

Really appreciate any help with this.
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Maybe try turning the new stop cock down a bit, see if that makes it the same as it was before?
I have tried turning down the new internal stopcock a few turn and it made no difference. But I had the outside stopcock off whilst I did it so maybe I opened that too far when I finished. It seems to get cold and takes ages to get really warm again when the tap amount is reduced
Two turns may not make much of a difference depending on how good the pressure is in your property, "example" my stop cock is open only one turn.
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Should I adjust at external stop or internal. Or not matter?

I have adjusted new internal stopcock so it only slightly open. Have opened about 2 turns. The flow is noticeably lower than before. However I still have the same problem when taps are fully opened. The water comes out lukewarm at best.

The issue does seem to be with the boiler. I had this problem with a very old boiler at my previous home but just coped with it by running the tap slowly. When I moved here I was impressed how well the DHW operated now it is noticeably worse.

Is there anything I can try ? Appreciate the help
Slowing down the cold water to the boiler is only masking the problem. The boiler will naturally slow the water flow through it to a rate that allows heat transfer as it passes through. If you need to slow it further, something is preventing proper transfer.

As you have already guessed, there is a good chance that cleaning your system has dislodged debris that has lodged in the dhw plate hex. They are great for collecting rust flakes from decaying rads.

Cleaning the hex, or replacing, may be your answer.
So I will need to call in a pro. Heat exchanger I imagine is pricey.

Will powerflushing clear the debris? Is there anything I can do to improve the situation I could do without shelling out hundreds on the boiler
Thanks for your help
Would advise RGI to test. If the hex is removed, will be obvious.

They're approx £100.
Is rgi essentially a service ? Do I have to specify an rgi? I was under the impression the usual boiler service was more like a safety check and didn't cover how well it was operating? The last time I had my old combi serviced he was in and out in a flash and did more harm than good. (The pilot kept going out, turned out after multiple visits he had put a hole in the flue or something)
RGI = Registered Gas Installer , ie someone qualified/registered to work on your gas appliance.
The last time I had my old combi serviced he was in and out in a flash and did more harm than good. (The pilot kept going out, turned out after multiple visits he had put a hole in the flue or something)

I take it that you won't be using him again? Ask friends, neighbours, relatives or colleagues if they know an engineer who is good. If not, consider seeing if Alpha do fixed price repairs or have an engineer in your area. Don't just take a stab in the Yellow Pages or with nonsense like Rated People.
Ha ha yeah hope he doesn't turn up again. It was on a service contract and he kept turning up to repair it after he had serviced. I lost patience after the fifth or sixth time (I'm a patient person) phoned and asked for another engineer who fixed it first time.

Don't know if its worth going with the same company again or whether to shell out on repair locally.

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