Plumbing, overflowing expansion tank

5150

Any plumbers out there?
I'd appreciate some advice.
Somehow hot water is getting forced up into the expansion tank in the loft from the hot water cylinder.
Have a thermostatic mixer shower with check valves on the supply pipes, and if I turn off the cold supply to the shower the problem goes away, but the shower is too damn hot ;-0
Can this problem be caused by air in the system or is it likely that the shower valve is faulty after only two years of service.
I should mention this problem began after our water supply was interrupted.

Cheers!

Gaz_Hammer

Hi,
I assume when you say check valves you mean 'non-return valves' or are they just isolating valves?
Is your cold water fed from the mains or tank?
What is the make of shower mixer valve? (probably not that relevant but might help in diagnosis!)

Sorry for all these questions but the answers will help!
Gaz

5150

Hi Gaz,
They're just isolating valves, the cold water to all taps and shower is direct from the mains and the shower valve is a Bristan.
The problem also stops if I leave one of the hot taps running a little, which seems to let the cold water out, then when the tap is "turned up" hot water comes out.

Gaz_Hammer

Hi again,
When the expansion tank gets hot is it due to overflowing water from the expansion pipe or is it that the tank water just gets hot?

If its from overflowing water than I would assume that the mixer valve is indeed faulty - Bristan products carry a 3 or 5 year guarantee! Look Here

Perhaps if Plumb1 reads this he may be more au fait with this product

Hope you get it sorted!
Gaz

john-306

For hot water to be coming out of the pipe into the feed/expansion tank then the cylinder is obviously overheating.
First check should be the cylinder stat either, faulty,set too high or not fitted correctly.
Reason it goes away when hot water taps are opened is coz you are replacing the water in the cylinder with cold water hence cooling the cylinder it till it heats up again but I'll pass on the shower part

5150

Thanks Gaz,
looking inside the expansion tank Its actually quite clear to see hot water coming up into it from the pipe connected to the hot water cylinder.
Maybe I'll contact bristan and see what they have to say for themselves.

5150

Thanks john-306, but even with the boiler shut down for several hours the process continues. So It seems the water in the cylinder is forced up to the expansion tank whether it is hot or cold.

john-306

Ah got ya now.
You running along the lines that the mixer valve cold supply is pushing the hot supply back up towards the cylinder and overflowing ? You should like you said be looking at the possibility of a fault on the mixer itself.Hopefully someone can help you out here.
Best of luck.

plumb1_2

Hi all,this sounds as if the the shower value is piped up wrongly
Unless it a presure balancing shower,if it is,it the non return values inside the shower that faulty.you can order here


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,Bit if not.It should be of equal pressure,s,ie both hot and cold feed from the cold water storage tank.I has been stated that the cold feed is piped up from the cold mains,that should not be the case,(as i suspect it s the wrong spec shower value)need to know the model.
even though it has worked for a period of time,what has probaly happened is that the non-return valves in the shower value (hot side)has started to bypass thus allowing the cold(mains pressure)to feed through to the hot supply,pass back into the cylinder and up over the expansion,into the tank.

5150

Thanks plumb1,
Can't remember the model name, but from looking at the Bristan website it looks like an osborne, although I don't rmember it costing quite as much as that.
maybe its a cheaper discontinued version?
I do know it's got some kind of little plastic inhibitor thing fitted inside the cold water inlet (but not the hot) if that means anything.
Looks like I'll have to search the attic for the box etc before going any further.

5150

Well,
I braved the attic and discovered the box and amazingly the manual too.
So, it is an Osborne thermostatic, and the specs state that its suitable for use in "Gravity Fed Hot and mains cold (Differential Pressure)"
Reading further it states that the check valves are located in the elbows. Plumb1, I presume these are the non return valves you refer too?
I'm hoping these can be replaced by a non qualified bod like me;-)
Thanks for your help everybody