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Water not heating after system drain - not airlock(?)

Discussion in 'Plumbing and Central Heating' started by JPreston, 19 Nov 2015.

  1. JPreston

    JPreston

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    Hi all - first post from me but long time lurker - any advice gratefully received...

    After draining my water tanks and pipes in order to move appliances round a new kitchen, my gas boiler no longer heats my water cylinder. Cold water flows steadily from my hot taps. Gas central heating works as it should.

    I read that this is a common problem caused by an airlock after draining, and so followed the advice to clear this - connecting a hose from the cold mains appliance outlet to the neighbouring hot appliance outlet and running mains back up into the hot pipes. I was alone the first time I did this so I wasn't able to watch for any bubbles in the cold water tank in the loft at the time. When repeating this with a helper, up in the loft I can see this causes the level in the cold tank to rise (any bubbles will have long since cleared). So I don't think I have an airlock between the hot water cylinder and the cold tank in the loft.

    Furthermore the hot cylinder seems full, because the immersion heater works fine. After using the immersion heater hot water comes steadily out of all the correct taps. So I don't think I have a problem between cylinder and taps either.

    If I hadn't just drained the system, I would have guessed the problem was either with the three way valve (or the controls). The pipe going to the three way obviously gets hot as is what I assume is the pipe going to the radiators, while the pipe going from the three way to the cylinder is cool. But, I feel crazy talking about the motorised valve when I know that the system was just drained and the problem occurred immediately afterwards and ever since. Yet I have done what is advised to clear an airlock and still no luck.

    The only other thing that might be relevant is that originally I tried to isolate the cylinder (to avoid having to drain the whole system). I tried to turn a valve on some 15mm pipe going into the bottom of the cylinder using a spanner (valve wheel is missing) - but it was possibly jammed. I thought it was turning when I was closing but now it comes to opening it up again I see that I was probably just spinning the spanner around on the shaft. In any case, going into the bottom of the cylinder as it does this pipe must be the cold feed in from the loft(?) and the cylinder seems to be filling OK, so I guess this valve is open, and is not the problem.

    Could it be some safety mechanism on the motorised valve preventing the cylinder being heated while drained, that I need to reset somehow? Or is there something else I need to do to locate and clear a remaining airlock?

    Any advice gratefully received!
     
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  3. gas112

    gas112

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    Sounds like You have snapped the balancing valve on the cylinder so the heating/hw circuit will now need draining and it changed
     
  4. JPreston

    JPreston

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    The stiff valve is a regular gate valve, it doesn't look like any balance valve that google throws out. Not sure if that changes your verdict?

    It is on what I now realise to be the heating circuit out from the cylinder (it comes out directly beneath the circuit in from the three way valve). I didn't make this connection before because the heat into the cylinder is 22mm and out is 15mm, not sure if that is normal.

    I now think I might have successfully closed it after all and not opened it afterwards, because that would explain the water not going around the cylinder I guess. I'll give a solid crank to open when I get home tonight. I might have rounded the square bit of the spindle somewhat so will think about how I can get a solid grip on it. I don't really want to have to drain the circuit and replace it, I have drained a CH system before, but it's getting cold now and with a toddler in the house I can't really afford to knock my heating out and have to wait for a plumber...
     
  5. 45yearsagasman

    45yearsagasman

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    It would be better if when describing what you have done, to post a pic of the relevant area. Saves a lot of guesswork.
     
  6. Agile

    Agile

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    If cold water came out of the hot taps then there was no airlock there and you totally wasted your time back feeding water into the cylinder!

    Its obviously a heating coil problem, possibly an air lock there.

    As for closing a valve when you have no idea what its there for then to me that is stupid. Touching any old gate valve risks it breaking and becoming jammed closed. You would never take medicine pills without knowing what they are for.

    Tony
     
  7. Agile

    Agile

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    You said your heating IS working ! So you would not "knock out the heating" whatever that means.

    You have an electric immersion heater to get hot water in a situation like this! So there is no panic and it can be fixed at any time over the next few weeks.

    Tony
     
  8. JPreston

    JPreston

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    I mean that if I were to drain the heating circuit, then I wouldn't have heating while it was empty and if I had problems refilling it afterwards...

    I should also stress that I did not drain the heating circuit, so would not have created an airlock in the heating coil, I guess. I was hoping to isolate the hot water cylinder from the downstairs so that I could move the pipes in the kitchen without draining both the hot and cold tanks beforehand. Yes with hindsight I shouldn't have touched the gate valve but I took it to be the hot water out from the cylinder to the taps (with it being 15mm) and were it not for man's indefatigable curiousity then we wouldn't have gone to the moon :p

    I'll post a picture or diagram later, thanks the suggestion and help above.



    By the way the switch for the immersion heater gets warm during normal use (I don't mean the heater itself obviously, the switch on the wall gets noticeably warm to the touch). Is that normal?!? I assume it's the fuse getting hot, it has a 13amp fuse fitted which hasn't blown yet, up to 3kW is 13amp I think and I can check the wattage later when I get. Assuming for now that it's the correct fuse should it actually get warm?


    Edit: all sorted now, it was the gate valve that I had in fact managed to close and get stuck closed. Apparently all plumbers love old gate valves because they are super reliable and never get stuck :D. A bit of plusgas penetrating oil, slacken the gland nut, tap body with spanner a few times, clamp the spindle hard with pipe grips and waggle back and forth until it would open fully. Then moved it back half a turn so its less likely to stick again. The heat(ed water) is o-o-on!
     
    Last edited: 19 Nov 2015
  9. DIYnot Local

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