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  • ALPHA CB24 hot water problem

    Hi. Our boiler has been working fine for ages but recently it has started causing us a few problems. When you turn the hot water tap on (downstairs or upstairs) it comes on but within a minute or two it goes cold again. You have to turn the tap off and try again, after a couple of goes the hot water comes back on only to turn cold again soon. I have checked the pressure on the boiler and its in the right place but for some reason the boiler switches itself off shortly after we turn the hot water on. Could you please advice what shall I do to get it back to normal. Thanks alot

  • #2
    hi claridge

    When you open up the hot tap and live it running does the boiler keep cycling by this I mean does it fire up and cut out then fire up again, if it does i would suggest that the dhw heat exchanger may be blocked. Removing it and cleaning this out should do the trick

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    • #3
      Originally posted by markhurst View Post
      hi claridge

      When you open up the hot tap and live it running does the boiler keep cycling by this I mean does it fire up and cut out then fire up again, if it does i would suggest that the dhw heat exchanger may be blocked. Removing it and cleaning this out should do the trick
      Thanks for your reply. I`ve just had a bit of play with the hot water tab and I`ve noticed unless you turn it on alot the hot water does not come on at all. Thats probably the reason the water in the bath is always hot because we always open the tab all the way. Obviously you can`t do that in the sink because the water will be splashing everywhere but once it gets cold it stays cold. Or if you turn it down it goes cold as well. Any ideas?

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      • #4
        Originally posted by markhurst View Post
        hi claridge

        When you open up the hot tap and live it running does the boiler keep cycling by this I mean does it fire up and cut out then fire up again, if it does i would suggest that the dhw heat exchanger may be blocked. Removing it and cleaning this out should do the trick
        hi again. in order to clean the dhw heat exchanger do i have to do all those things:

        4 DHW HEAT EXCHANGER - Refer to Fig. 26
        1. Gain access behind the casing and drain the boiler heating and hot
        water circuits as described in sections 8.1 and 8.2.
        2. Disconnect the three union nuts to the heat exchanger and remove
        heat exchanger by lifting it upwards from the rear right hand side 'O'
        ring seal connection.
        Note: Be careful not to allow water to drip onto any electrical
        components.
        3. Using the new washers supplied, re-assemble in reverse order.
        4. Refill and pressurise the system. (Refer to Commissioning, section
        5.1).

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        • #5
          yes but I would pay a gas safe registered engineer to do it should only cost an hours labour

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          • #6
            Originally posted by claridge View Post
            Hi. Our boiler has been working fine for ages but recently it has started causing us a few problems. When you turn the hot water tap on (downstairs or upstairs) it comes on but within a minute or two it goes cold again. You have to turn the tap off and try again, after a couple of goes the hot water comes back on only to turn cold again soon. I have checked the pressure on the boiler and its in the right place but for some reason the boiler switches itself off shortly after we turn the hot water on. Could you please advice what shall I do to get it back to normal. Thanks alot
            One of the most frequent callouts we have is to combination boilers with blocked plate heat exchangers. This is due to solid materials and sludge coming out of the heating system and lodging themselves in what is the natural bottleneck in any combination boiler system, the plate heat exchanger. We can clean this heat exchanger with the right chemicals, but I would thoroughly recommend the fitting of a magnetic filter such as a Fernox TF1, or a Magnaclean on the heating return pipework to take these solids out before they get to the boiler.
            My opinion is that you also have a DHW diaphragm that is due for replacement. This is why your boiler doesn't fire on hot water when you only have the tap open a little bit. Alpha diaphragms don't last very long, so this is quite likely. It's not a difficult job to change one, so don't pay the earth for it (should be no more than 60 or 70)

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            • #7
              Agree with all above but first port of call is your hot water flow switch which is clipped onto your diverter valve and just pulls off [no need to draindown]. Very common fault. Next would be the domestic hot water diaphram. Of course gas-safe engineer required.

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              • #8
                Thanks for all your replies guys, I best get a gas engineer in then

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                • #9
                  All of the above problems plus possibly the dhw thermister. You always need a registered gas engineer for these problems.
                  Colin Downs Boiler Maintenance. Newton Poppleford. Devon.
                  (01395)567306 colin(at)colindowns.net www.colindowns.net

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                  • #10
                    Hi
                    I got a gas engineer in and he told us we need new flow switch and he bought one & fitted it. I paid 95 in total and I don`t think this has solved the problem. I think the hot water lasts for a bit longer (i may be wrong) but after abit it goes cold again. Any suggestions and also do you think we have paid far too much for this little thing he fitted?

                    the flow switch looks like this one here - Google Image Result for https://www.pdqspares.co.uk/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/3/0/3013211.jpg

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