Hot water / Heating system woes? Bleed needed?

19 Sep 2006
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United Kingdom
Firstly, sorry to be a bit stupid posting here with fully understanding what system I have.
I have cold water feed in the loft.
Tank in airing cupboard
Boiler in kitchen (approx 15yrs old)
Boiler operates hot water and heating independently via wall switch thing.

A week or so ago, I turned of cold water feed into house and drained hot water by running hot taps. Reason being had a leak on hot bath tap, only way to cut water to it was drain system. I also made sure heating and hot water was off during this time.

All is good, until last night. When hot water came on after a few mins strange hissing/gurgling noises heard coming from boiler. They subsided after about 10 seconds, then happened again. I turned off the hot water and continued to heat via the immersion heater upstairs. Do I have air in the system, how can I remedy? The hot water seems fine.. warms ok as I checked before turning immersion on. No sputtering from taps.

Heating... No problem here, the only minor this is that there is 1 particular radiator (top of stairs/landing) that needs bleeding possibly weekly as its half full of air. Is there another way of bleeding the heating system.

Sorry im vague about my system. Unsure how I tell what I have. Can get some photo's if necessary

Ta in advance
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There is no physical connection between the water in the hot water cylinder and the water in the boiler and radiators. The two systems are kept separate. The hot water cylinder has a coil of pipe like a radiator inside that the boiler heats. Similar to the way a radiator heats a room Here's a diagram.

Drawing hot water off via the taps until they stop running doesn't drain any water from the boiler, and not even the hot water cylinder is emptied as water is drawn off from the top of it. The cylinder remains full when water stops running from the taps.

So what you did would have no effect on the water in the boiler, unless you have a ancient primatic cylinder (40 years plus old) which is a different kettle of fish. A primatic cylinder only has one cold water feed tank in the loft instead of the two shown above.
Thank you very much Stem for the detailed information.
That looks how my system is set up.

Well, not sure what the noise is :confused: , I shall see if it is still making it when I heat the water later.

Is it possible to cure the rad that always gets air in?
Is there a general vent for the heating system?

Many thanks
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This is a common problem but not always easy to fix. Air (or gas) can be produced because of corrosion of steel radiators or cast iron boilers. Black sludge in the radiators is also produced. A system flush and addition of a corrosion inhibitor can prevent this. More information here Or the system could be pumping over and introducing air in the process.

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