Hot water from combi condensing boiler

Discussion in 'DIY' started by annie1969, Nov 20, 2012.

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  1. Anyone know how to help? The boiler is a combi condensing boiler and the water comes in from the mains. In the summer the hot water is hot all the time but in the winter the water runs hot and cold so you can't get a hot shower or a hot bath. I think this happens cause the water is too cold when it's coming into the boiler. Is the only way to sort this to install a cold water tank to feed the boiler? I've tried adjusting the water temperature but it makes no difference. Any help greatly appreciated as the two gas engineers have been worse than useless. Thanks
  2. If your combi boiler is mains fed it should give hot water on demand ? It could be a problem with flow rate/pressure, do you have a make or model number of your boiler ?
  3. I'm not sure a water tank will help as most boilers are fussy about the pressure of the incoming feed. If the water's hot in the summer, but runs hot then cold in the winter then the boiler may be overheating before it gets your water to the required temperature, cuttings out, then reseting.

    Check any indicators on the boiler and give the manufacturers or importers a call. There's also quite a few DIY/Trades forums where you might find it mentioned.
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  4. As above - The pressure of the incoming water supply and also back pressures from your taps and fittings are critical, the boiler shuts down to protect itself/you if the flow rate is too low.

    I would change the water filter element first off and then check the perlators & shower heads, these should all be the correct type for your boiler and be free from calc. If that doesn't help then its a problem with the combi boiler.
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  5. Combo boilers suck 4k spent three years ago on one and every winter the bloody thing goes tits up and the pipe freezes up no matter how I cover the pipe.
    British gas want £1000 to move all the pipes in to the loft space what a con job.
  6. Which pipe?
    Is it the condensate drain?
    Did BG install it?

    The insulation only slows the rate of heat transfer from the pipe to the air, so a long freeze will eventually freeze a cold water pipe, if there is no heat entering the water. Exposed pipes should be trace heated to ensure they don't freeze.
  7. Combi boilers should only be mains fed. There is usually a pressure gauge on them that sometimes needs adjusting. Have you checked that?
  8. A cold water tank is not the solution, the boiler is meant to be supplied from the mains.
    I'd think there's a problem with the heat exchanger, the diverting valve or the gas setting, but I don't know.

    I'd suggest you copy and paste this, with the boiler make and model number, onto a specialist plumbing and heating forum.
    All the plumbers will be out plumbing, ripping off grannies, weeing in water tanks, etc..

    Try this one; Plumbing and Central Heating Forum - - DIY and Home Improvement
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  9. I've had mine 20 years, other than a few break downs it's been great and of course very economical until they hiked gas prices.

    Posted from the ARRSE Mobile app (iOS or Android)
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  10. Have you checked where the air coming into the system is being drawn from? If for instance your nextdoor neighbours chimmney is too close to yours then you might be drawing hot air into the system which will cause it to overheat and switch off.

    This would explain why it only happens in the winter as well.

    Just an idea.
  11. But is that acually a condensing boiler? I thought these were a more recent development, and full of unreliable electronics. I've also had a combi boiler for about 20 years with only two minor repairs, no electronics in it at all. Also no condensate drain, these seem to give a lot of trouble on condensing boilers, often due to incorrect installation.
  12. The pressure gauge indicates the heating system pressure, if that falls below the pre-set limit - normally about 0.4- 0.5 bar then the sytem will simply shut down to protect itself, it will not cause the op's symptom which is related to the hot water side of the system and undoubtedly linked to the metering/ flow control valve.

    I had exactly the same symptoms, my system worked perfectly for 3 months after installation in the summer, it took weeks to fix after attempts by the installer and the combi rep, it turned out to be the metering valve spindle fitted the wrong way around somewhere along the line and took a whole 10 minutes to fix once the manufacturere sent out an engineer. I was very suspicious to be honest, the glow worm engineer did no checks whatsoever, walked up took the cover off removed the valve spindle turned it around and inserted it back in then started the boiler back up and told me it was fixed, when I asked if it was a known fault he replied no, just a lucky guess as he had seen it before, I then pointed out that he hadn't tested if it worked yet and he looked very embarrassed. Sure enough it was fixed and we've (touch wood) had no problems for 3 years.
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  13. It should be running at about 1.5bar - any lower and the temperature will drop on all systems as it tries to compensate. Adjusting this should be in any O&M manual that came with the kit, or as an idiots guide somewhere on it.
    Failing that, inevitably there will be someone doing this on Youtube so go and have a gander on there.
  14. I tend to keep away from repairs, mainly installs, but there are a number of things it could be.

    Mains water is much warmer in summer than winter...... try turning the flow of water into the bath a little lower, I know mine gives hotter water that way.

    Does the boiler burners shut down and the fire up again, constantly cycling?

    Most boilers have their own unique problems... as Onetap says, one of the forums might be able to recognise the problem.

    If you give much more information, boiler make etc. I can try one of the installer only sites.
  15. It's a Vokera Unica 36HE