curious behaviour of hot water system

I have a single cold water tank in the roof, an indirect hot water cylinder and a wall mounted Potterton gas boiler.
The central heating pump has a standard 1" pipe into the bottom, and a converter to a 1/2" pipe at the top. Actually, the pump seems to be mounted upside down...
Anyway; the bottom, 1" pipe circulates the centrral heating water AND the water into the cylinder coil. Both the cylinder and the main CH pipe have electronic valves on them.
The problem: periodically during the day what sounds like a large volume of air enters the system. The hot water vents into the roof tank to truly alarming noises.
I've changed the cylinder thermostat; changed the programmer; taken all the radiators off, flushed them through and refilled the system. But the problem remains.
Can anybody advise me please?
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For your problem, we Yanks are as useful as teats on a boar. You need our Brit plumber, Christian.
MM
MM
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wrote:

Let's hope he surfaces. I didn't realise this was US orientated group - it's the only plumbing-specific group on my feed. Interesting, though...
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All the brit plumbers hang out at uk.d-i-y

our Brit

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Although Ime not the brit plumber I am a brit and know a little about plumbing...but I agree with you that what we need is a brit plumbing newsgroup! First of all you might find this website useful.....its British http://www.gasman.fsbusiness.co.uk /
This problem brings up more questions than answers I am afraid.... has it always happened or is this just a recent happening? When there is a surge is this into the central heating system expansion tank or the cold water storage tank and is this air, is it water, and how long does it last? Have you recently had any pipework installed or changed. I found to my cost that moving pipework to simply make things fit better causes all kinds of unexpected problems? One example is contained in the website which explains the right and wrong way to fit the cold water feed to the central heating system and its proximity to the expansion pipe for the same system, any distance variation or location change causing ingress of air and excessive corrosion. Have you recently changed the speed of the pump? You say the pump looks like its mounted upside down. There should be an arrow on it to indicate the direction of flow which should be out to the control valves and from there to the cylinder coil and the central heating. My initial thoughts are that it happens just as the pump switches on (since both the cylinder stat or central heating stat will switch it off) and as either stat switches on the pump suddenly starting causes a surge of pressure, but only momentarily and it would probably happen if the pump was set to full speed.
Answers to the above questions might indicate better the cause of the problem.
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IS THE BOILER THERMOSTAT UP TOO HIGH OR FAULTY? CAN CAUSE YOUR PROBLEMS
RENE (ESSEX UK)
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