My central heating system has a cylinder and a small tank in the loft so I think it counts as 'open vented'. I don't go into the loft too often but I have noticed that whenever the heating is on, hot water gushes quite fast into the small tank (which I presume is the expansion tank). See photo. The water doesn't overflow, so presumably it is returning to the system by another pipe which runs from the base of the tank. It's not a trickle; the hot water is pouring in steadily at about a pint a minute. Is this right? I was under the impression the expansion tank was a sort of pressure relief system that only operates in some circumstances.
Cataract in expansion tank
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It's very wrong.
Assuming that it didn't do this when it was new, there is probably an accumulation of sediment blocking the correct circulation of water through the pipes. There's a chance you can loosen it with a chemical cleaners, which would cost about £15 and is an easy DIY job, so worth a try, but more likely you will need to locate, cut out and replace the blocked pipes.
The blockage is probably where the 15mm feed pipe from the small tank joins the large circulating pipe. This may well be next to your hot water cylinder. Post some pics of the pipework please.
Have you got a magnet? Run it along the copper pipes and see if it attracted to an iron deposit where I suggested.
p.s.
look for the pump and photograph it please. There is probably a small plastic adjusting knob on the square box.
pps
unless you can do simple plumbing, ask around for a recommended local plumber or heating engineer (this repair does not involve touching the boiler)
Assuming that it didn't do this when it was new, there is probably an accumulation of sediment blocking the correct circulation of water through the pipes. There's a chance you can loosen it with a chemical cleaners, which would cost about £15 and is an easy DIY job, so worth a try, but more likely you will need to locate, cut out and replace the blocked pipes.
The blockage is probably where the 15mm feed pipe from the small tank joins the large circulating pipe. This may well be next to your hot water cylinder. Post some pics of the pipework please.
Have you got a magnet? Run it along the copper pipes and see if it attracted to an iron deposit where I suggested.
p.s.
look for the pump and photograph it please. There is probably a small plastic adjusting knob on the square box.
pps
unless you can do simple plumbing, ask around for a recommended local plumber or heating engineer (this repair does not involve touching the boiler)
The small tank is called a Feed and Expansion (F&E) tank.
For the feed side, it feeds cold water into the boiler's primary pipework system to make up for any losses from evaporation, tiny leaks etc.
The expansion side is catered for by the big pipe (normally 22mm), from which water is running in your photograph. When water is heated from 0 to 100 degrees Celsius, it expands by about 4%. The expansion pipe should direct this water (or any excess not contained within the pipe itself) into the F&E tank. In a fully pumped system, this loop should be a minimum of 450mm above the F&E tank water level to also accommodate any surge when the pump turns on.
The expansion pipe should not have water running from it during normal operation of the system. I would suspect there is a blockage in the system somewhere, most likely in the cold feed from the F&E tank, or that the pump speed setting has been turned up too high.
For the feed side, it feeds cold water into the boiler's primary pipework system to make up for any losses from evaporation, tiny leaks etc.
The expansion side is catered for by the big pipe (normally 22mm), from which water is running in your photograph. When water is heated from 0 to 100 degrees Celsius, it expands by about 4%. The expansion pipe should direct this water (or any excess not contained within the pipe itself) into the F&E tank. In a fully pumped system, this loop should be a minimum of 450mm above the F&E tank water level to also accommodate any surge when the pump turns on.
The expansion pipe should not have water running from it during normal operation of the system. I would suspect there is a blockage in the system somewhere, most likely in the cold feed from the F&E tank, or that the pump speed setting has been turned up too high.
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Easy just check pump speed first if it's on three turn it down to two have you had a pump changed lately?
First of all, the system has been there for a long time and has never been DIY'd; it has only ever been touched by professional plumbers.
The pump has indeed been changed recently (5th August); on the annual service the plumber told me the old one wouldn't last the winter. The system has had Fennox filter attached to it for the last 5 years and the fluid (whatever it's called) was replaced this August as it had reached its five year anniversary; so unlikely deposits have built up to a degree to cause a blockage. However, what is possible is that the plumber has shut a stopcock that should be open or opened a stopcock that should be shut! This firm has made occasional errors like that in the past in the past and I posted one of these not long ago (solved by you people!).
I am posting pictures from the inside of the airing cupboard showing the three taps I can see (the one above the pump doesn't have a handle). The pic from the top of the airing cupboard shows two taps with handles. The left han d one goes into the gravity shower in the bathroom (cold feed from tank I think). The right hand one is on a pipe going into the loft.
There is at least one more tap up in the loft...I can post photos of the loft if it helps.
More info...I've spotted a couple more taps in the airing cupboard I didn't notice before; one below the pump, the other marked 'c/w feed c/heating'. I still have a suspicion that one of these various taps is incorrectly open or shut...if someone can confirm the correct setting for each I can check. Or should they all be open?
One more thought....googling took me to a site called diyplumbing.co.uk. According to this the most likely causes of Pumping Over are pump speed too high (already mentioned) and 'The pump has been installed the wrong way, and is directing water the wrong way around the system'.Can I diagnose the latter from the outside?
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Had the system been installed correctly then pump speed won't be an issue...
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