Help - Expansion tank overflowing regularly - driving me mad

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1 Feb 2009
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Humberside
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United Kingdom
1. Boiler is an aged Glowworm but still works great
2. Expansion tank is filling from the hot water cylinder it seems, as water is hot when heating/water is on, otherwise it still fills but cold. It then runs from the overflow outside.
3. Started earlier this week, but nothing had been done work wise except a few days earlier I had upped the stat a little due to the inclement weather 9from about 140deg F to about 160deg F.
4. Having read everything about this issue, I suspected the cylinder coil was leaking so I've fitted a new cylinder but it's still leaking from the overflow. (£200 wasted 'cos I'm dumb!!)
5. Don't know if it's related but ever since I had my bathroom redone about 4 years ago, two radiators downstairs have failed to heat up properly. Since I changed the cylinder yesterday, they aren,t heating up at all. I have removed them and cleaned them out several times; flushed the whole system several times. The rads concerned always refill OK and have previously warmed up (tops only) so I can't see it's a blockage.
My system is gravity fed with a small CW feed tank to the heating circuit and a large F/E tank for the hot water cylinder. It has a two-port valve for the heating circuit and a small Grundfos pump which I cleaned out a few months ago (it was seized with crap inside). Just looked at the pump and noticed the writing on the cover is upside down. Not sure, but it's possible I've put it back on upside down, although this overflow problem has only just started and did the pump months ago.

Any advice would be much appreciated. I'm not a plumber by trade, but I would like to at least have a go myself first, so advice on any testing etc. to locate the cause would be great.
 
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Have you tried turning the pump down to 2?

If there is a constant overflow from the FE tank, check the obvious that the valve is closing properly and that the ball hasn't burst, letting water in - happened to me recenty.
 
without keep reading that mumble jumble.

your cws tank is filling and over flow running.

shut your mains stopcock if it stops you have a faulty mixer tap or shower valve passing cold mains to hot gravity.
 
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Thought it was the FE tank overflowing - hence why suspected split cylinder coil.

Can't see how mains water gets into the FE tank! :confused:
 
its not. its going into the cws.

cylinder coil its a brand new cylinder.
 
Expansion tank is filling from the hot water cylinder it seems, as water is hot when heating/water is on, otherwise it still fills but cold. It then runs from the overflow outside

?
 
My system is gravity fed with a small CW feed tank to the heating circuit and a large F/E tank for the hot water cylinder.

you have to read between the lines sometimes on what people call things.


it may not be the fault but as i said earlier its mumble jumble. so just try to guess what they mean.
 
op's don't always make it easy to locate a fault as the descriptions can be very limited.
ok-wink.gif
 
A big thanks to seco services in particular. It never occurred to me, but it definitely looks like it's my shower mixer, 'cos with CW mains supply off, the tank doesn't fill, but it does as soon as it's back on.
Anyway at least I know where to go next.
 
showers can be a problem.
but is your shower fed from cold mains gravity hot ?

common one is the kitchen mixer which will be cold mains hot gravity.
or any bath mixer etc.

can you isolate one at a time to see ?
gros10-1.gif
 
Fortunately, my kitchen mixer is less than two months old and it's one of those mix in the downspout types, if you know what I mean, so I don't think it's that.
However, my shower mixer is a thermostatic valve jobbie and when I checked the hot water side goes ice cold only a second after the shower is turned off so I'm confidant it's the problem.

I'll replace it tomorrow.

Once again, a big thank you. If you'd been in my area you would have just won yourself a customer ( 'cos my radiators still don't work and I guess I need some powerflushing or the magna-do-da treatment!)
 
However, my shower mixer is a thermostatic valve jobbie and when I checked the hot water side goes ice cold only a second after the shower is turned off so I'm confidant it's the problem.
im amazed it works properly on unbalanced pressures.

gros10-1.gif

your rads i would say are airlocked in the pipe drop downs and need balancing properly.
 

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