Attic water tank overflowing

Darwin

Hi, apologies for this post on christmas eve and also for my novice understanding of plumbing matters. We are having a problem with our water tank in the attic - our house is a dormer bungalow so the attic space is tiny. We had a pump installed in the downstairs hot press about 2 years ago which give us better water pressure in the shower and taps and also refills the water tank in the attic. The issue is, the water from the attic tank very occasionally seems to spray upwards with some force (wetting the rafters just above and also the inside felt of the roof) and pools over one side. This happened just now and on two previous occasions in the past year:

1) When flushing the downstairs loo rather vigorously
2) Two days ago running the hot water tap in the bath for about 5 minutes (we never use the bath, just the upstairs shower)
3) Again today, I had the washing machine on and my wife was having a shower. Our washing machine has two separate feeds for hot and cold water supply.

The pump/water tank has been trouble free otherwise, no issue when showering or doing the washing up in the kitchen with hot water. It seems creating a situation where there is a large water demand from the attic tank causes the issue. I've switched off the pump for now. Is it possible the plumber has overlooked something during installation e.g. pump pressure too high? I'm hoping and praying it doesn't overflow anymore until I can get someone to look at it. Thanks in advance and happy christmas everyone.

K.Flyer

First off the pump in the hot press that boosts the pressure to the taps and shower does not also refill the attic tank.
It could be one of a couple of things.
It may have an issue / fault with the ball cock filling the attic tank.
What I would suggest is get up to the attic tank and press down on the ball cock and see if any water shoots out of the body of the valve.
If that's not the problem, then it may be condensation that you see on the felt / rafters.
How do you heat water, do you use the immersion?
How hot is the water at the taps?
If you are using the immersion to heat water it could be overheating due to a faulty thermostat causing condensation to occur above the tank.
It could also be central heating related if you have what is referred to an open vented system and you are getting the occasional pitching occuring.
But check the first two ideas and see if you find anything.

Darwin

@K.Flyer thanks so much for your help and suggestions. I got up on the ladder to the attic while the shower was running to try and see what was going on. It turns out the water inlet valve (?) is sputtering like crazy when the tank is refilling so the water jets out over the top of the tank. I put a piece of cork over the top of the tank and that seems to contain the problem for now. I pressed down on the ballcock and the water didn't leak on the outside valve. At least the water tank isn't overflowing I guess! I presume a new ballcock assembly will solve the problem?

listermint

New ball cock and valve will solve.