Hot/steaming Feed & Expansion tank.

21 Oct 2005
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United Kingdom
Up in the loft this morning replacing a float valve on the cold water tank I noticed that the feed and expansion tank was hot/steaming. When the main hot water tank was heating there was a continual hot water flow into the feed and expansion tank from what looks like a vent pipe. The steam in the tank is finding its way into the overflow pipe, condensing and then dripping outside.

Is it normal for the feed and expansion tank to get hot. If not, how/why is hot water finding its way into the tank ?

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Not normal, but quite frequently encountered :evil:

You need to have the heating system pipework looked at, particularly just before the pump. And is the pump on the right way around?

What system do you have?
Glow worm Ultimate boiler, with what I can see to be an open vented system.

Not had the system apart. Other than the above fault, it would seem to be operating normally.

Layout very similar to this -

Check the pump is the right way around (no.4) and that the output from the pump goes to the AB port on the valve (5)

That must be a really old book because not since the old Drayton 3 port valve has the flow come into the side of it. :LOL:
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Hi there,

I'm new to this forum and a bit of a novice with central heating systems, but I seem to have the same problem as Golden Rivet. The feed and expansion tank is getting steaming hot whilst the hot water circuit is being heated. This is caused by hot water coming up the vent pipe (the pipe feeding into the top of the tank). The system is the same as in the picture provided by Golden Rivet except that (a) the pump 4, feeds into the bottom of the valve 5 but the priciple appears to be the same,and also (b) where the air seperator 3 is marked, I just seem to have a T-piece.
The system has not had any work done on it and appears to be working fine in every other respect, but the problem is causing some condensation in the loft.

Also just noticed that the hot water does seem to be very hot!

Any thoughts on the subject greatly appreciated.

Many Thanx,


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