Overflowing Expansion Tank = Wet Floor and Worrisome Wife.

yeahdisk · 25 Apr 2009

Last night I was alarmed to find water dripping out of my loft hatch! Turns out the CH expansion tank was overflowing (the overflow pipe to the outside world must have had an airlock or something because when I tapped it a few times it started to work again and the water ran off).

Its a conventional boiler with HWC, cold storage tank and smaller CH expansion tank.

The Ballcock Valve in the expansion tank is working fine and cuts off when there is about 2 inches in the bottom of the tank. There is a further 6 inches (about 10 litres worth) of room to expand before the level would reach the overflow. Does this leave the Boiler Vent as the culprit? How would I remedy this situation?

Another issue that I discovered whilst up there, is that in the Cold Storage tank, the HWC vent outlet is beneath the water level by an inch? Is that correct?

I guess the first thing is to redesign the overflow pipework to prevent airlocks in the future, but then what?

All help appreciated, I really don't fancy a wet floor again!

twgas · 25 Apr 2009

do you get pumping over when the CH is on?

yeahdisk · 25 Apr 2009

thanks for the reply

Well the CH is on anyway and there's been not even a drip out of the vent. I even turned the CH pump up to 3 (its normally on 2) and turned the boiler thermostat up, still not even a squeak out of the vent.

Yesterday I had a pretty long shower (power shower) about an hour before the overflow started. From my limited knowledge I don't see how this could be relevant, but do you think this could have something to do with it?

seco services · 25 Apr 2009

has it not filled since ?
was the water in the tank warm/hot when it was overflowing ?

yeahdisk · 25 Apr 2009

yup it was hot when it was overflowing.

After I had solved the airlock problem I bailed out the tank to the correct level (i.e. I removed water until the ballcock valve started spewing out water which means there is approx 3 inches in the bottom of the tank.) The level of water has not gone above this since.

seco services · 25 Apr 2009

shower shouldn't of played a part in the overflowing.

hi1 · 25 Apr 2009

Coil gone in hot water cylinder?

seco services · 25 Apr 2009

hi1 said:
Coil gone in hot water cylinder?

poss
but a failed coil will useally keep filling the f/e not just a one off.

hi1 · 26 Apr 2009

Tap or shower letting by then? He states he had a long shower prior to tank filling and over flowing?

seco services · 26 Apr 2009

he had a long shower then he would of had to have a bypassing shower,
+ a faulty coil to backfill the f/e.

tryitandsee · 26 Apr 2009

My long shot....Is your float arm straight, so that the float goes easily up and down with the rising and lowering of the water level.

Sometimes when the ball cock is put in place they are slightly off/turned, the result being that the arm gets stuck on its way back up again (especially when you have nearly emptied it, thinking of your power shower.) Chances are it would never happen again just bad luck. For the sake of a new complete ball valve/float/arm etc. I would change it.

tryitandsee · 26 Apr 2009

Oops, just re read it again......it was the expansion tank that over filled

tryitandsee · 26 Apr 2009

Another issue that I discovered whilst up there, is that in the Cold Storage tank, the HWC vent outlet is beneath the water level by an inch? Is that correct?

That does not seem right, would it not syphon back down.

tryitandsee · 26 Apr 2009

When power showering, if the vent is turned down into CWS an inch below water level would this then syphon water back down into the hot water cylinder and then start filling the expansion tank (as the CWS tank water level is higher than the expansion tank.

IMHO increase the hight of the vent pipe getting it clear of the water.

seco services · 26 Apr 2009

tryitandsee said:
syphon water back down into the hot water cylinder and then start filling the expansion tank (as the CWS tank water level is higher than the expansion tank.

how would water from the cws start filling the f/e they are both seperate.
unless the coil had failed.

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Overflowing Expansion Tank = Wet Floor and Worrisome Wife.

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