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Recurring air lock in hot water

Postby silly-diva » Mon Dec 22, 2008 9:10 pm


I have just moved in to a rented flat and when I got the keys there was no hot water coming out the hot water taps in the kitchen or bathroom. The plumber came out and told me there was an air lock in the sytem which he fixed. Unfortunatley taking the air out only seems to work for a few days - the same problem has returned 3 times and I'm without hot water again tonight :(
My plumber doesn't seem to know why this is happening. I see from reading articles that a recurring air lock can be caused by the tank emptying faster than it fills up. He has already checked for this including the valves and he says everything looks fine. It seems to happen in the evening after the system (which includes my central heating) has been on for a few hours. I turn on the hot water tap and nothing comes out! I do seem to get some water during the day when the system hasn't been on, however the pressure is very poor and often stops after running after a bit ( I can't get a full sink out of it).
I don't know very much about central heating systems, but my gas boiler is an FEP Care Gloworm Fuelsaver F.
Does anyone have any idea what could be wrong? Is it possible that my lack of hot water is something to do with overheating due to the system being on for a certain amount of time? And can washing machines cause air to get in?

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Simply Build It

Postby C23kW » Tue Dec 23, 2008 1:09 am

hi there, am not an expert about this topic. But maybe it could be gradients on your pipework that is the problem, it may rise upwards then down and create an air lock. however if you got a qualified plumber out then he would have noticed. just a thought...

thanks CkW
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Postby nitro23456 » Tue Dec 23, 2008 7:26 pm

so its that no water comes out your hot tap at all? not, that is just cold?

The former is likely to be an airlock or blockage in the cold pipe from the loft tank to the bottom of the cylinder..... check any isolation valves on this run are fully open and havent seized closed (slightly) as this would mean some water would get through. The same goes for the pipework out the top of the cylinder.

Is this all hot taps or just one in paticular?

How about getting someone to see if CW tank in the loft is filling quickly enough to subsequently replace the water drawn off the cylinder when the tap is opened - this would rule out a problem before the tank.

The task is to identify where this happening exactly between the loft tank inlet and your hot tap. A remedy can then be advised.
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Postby bobplum » Wed Dec 24, 2008 8:50 pm

this may seem like a mad idea but if you have or can get a wet and dry vacumn stick it on wet connect hose to say kitchen sink tap open tap turn on vac and suck out blockage/airlock,make sure the hose is tight on the tap i know sounds crazy but it does work and lets be honest you have nothing to loose
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Postby silly-diva » Sat Dec 27, 2008 9:12 pm


Thanks for your replies and hope you've had a nice Christmas!

Just to clarify, it's my kitchen tap (which is just below where my hot water tank is stored) that seems to get affected the most as it runs to a standstill when the air is in. Some hot water manages to get out the bathroom taps but the pressure is very poor and eventually stops.

A plumber came on the 23rd and removed the air lock and the supply was back to normal. I let the water run for several minutes on his instruction so the air would go completely.
I've returned from being away for a couple of days and just used the washing machine - I've now noticed that I'm getting less hot water!!! I think it's just going to go back to the way it was. This is the 4th time in 4 weeks. The most recent plumber said he thinks it may be something to do with my hot water tank as it's old. The plumber before that checked the tanks in the loft of the tenement and said everything was normal, although he didn't let my supply run and check how it was refilling.

I'll need to get back to my letting agents on Monday and moan at them again. There is no use is calling out the contactor to take the airlock out when it's just going to come back - I really need someone to get to the root of the problem. I have been kindly given a rubber hose by one plumber however I'm not supposed to fix it myself as it's the letting agent's responsibility. Also, if I break something they'll take my deposit quicksmart, even though it's OK for them to let out a property with a faulty hot water system!!
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Postby plumbbob » Mon Dec 29, 2008 11:08 am

I would go with Nitro's suggestion tha the feed to the hot water cylinder is restricted in some way which means when you turn on the hot tap, air is drawn down the expansion pipe causing the airlock.

If you have mixer taps in the kitchen, by putting your thumb over the spout and turning on full the hot water then the cold, will force the air back up the expansion and clear the airlock. Do this for at least 20 - 30 seconds.

If this cures the airlock and the hot water flows, only draw off hot water slowly until the cause of the blockage is found and repaired.
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Postby stoneyboy » Mon Dec 29, 2008 4:31 pm

Do you happen to know if the cold water tank in the loft serves only your apartment?
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Postby SweetBriar » Tue Dec 30, 2008 8:36 pm

It may be some scale from the cylinder has blocked the pipes? Is your kitchen tap a mixer or 2 seperate taps? If its a mixer, you can use the cold mains water to push back along the hot water pipes.....
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Postby TheDoctor5 » Thu Jan 29, 2009 12:28 pm

If you type the key words of your question into our search box to the left of the site you may find the answer is already posted or is in the DIY projects section of the website. Every post goes through a monitoring process and using the search box may speed up your answer.
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Postby Shakes » Sun Aug 02, 2009 8:10 am


If you have mixer taps in the kitchen, by putting your thumb over the spout and turning on full the hot water then the cold, will force the air back up the expansion and clear the airlock. Do this for at least 20 - 30 seconds.


After spending hours trying different things and getting nowhere I tried this solution and it solved the problem. Even impressed the wife! Thanks.
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