Should Feed and Expansion tanks bulge?

[Mike Dodd]

Ongoing situation at "Big Sister's" house...

I asked in here a few months ago about various problems with Big Sis's plumbing, however, time moved on and her leaking plumbing disappeared and she set her sights on getting the whole plumbing replaced when she could find a plumber prepared to take on the job...

Then, yesterday, her leak came back with a vengance.

She apppears to have an indirectly heated hot water system (standard cylinder, 3-port valve, boiler downstairs, water pump etc), with a feed and expansion tank installed a couple of foot above the cylinder, all contained within an airing cupboard type of arrangement.

The leak appears to be coming somewhere from the Feed and Expansion tank. Unfortunately, this sits on a piece of delaminating plywood which acts as a sponge, so wherever the leak is, it drips into the plywood which distributes is over the complete area of the airing cupboard making tracing the leak very difficult. Coupled to the fact that the F&E tank size is pretty much the internal dimensions of the airing cupboard makes the whole thing a right bugger to work on.

Last night, having fused the CH circuit from water dripping onto the electrics (sigh!), I went around to take a closer look. Having removed the architrave surround to get a glimpse of the feed (and overflow) pipework going to the F&E tank, I was somewhat alarmed to see that the side of the tank that takes the feed/overflow buldged to an extent that there was a horizontal deflection of some 4-5 cm halfway down the side of a 50cm tall tank.

To me it looked wrong, and could indicate where the tank has failed / is leaking. but until I can get there as a respectable plumbing time (i.e. not 9pm, and when I've charged my torch [hate it when they die after 2 mins use], and when I've got a set of step-ladders with me) I couldn't investigate further. In fact, I'm of the mind to replace the tank anyway.

So, to a question or two...

Is it commonplace for F&E tanks to incorporate such a large "buldge" in the design. Is it the considered opinion of those that deal with such stuff that this is likely to represent the point of failure of the tank?

How much would a replacement tank cost (existing tank approx 80cm wide,

50cm deep, 50 cm high)? (I've tried online but there're few hits on F&E tanks, closest I got was loft tanks in Screwfix) [actually, cold light of day, their "10500" 25gal tank looks ok - is a loft tank the same as a F&E tank?)

[dom]

How many connection points on the tank? Presumably feed (with a ball valve), outlet and an overflow. Water level is probably below 2 of those, so either the outlet leaks, the coupling to the ball valve leaks (which is presumably full mains pressure) or the tank is split. Must be a substantial leak to fuse the electrics. I'd expect a pvc tank to deform considerably before it would split, but it might cause a leak round the tank fitting if it's been badly placed.

[Dave Liquorice]

Not in my experience. As this tank is in the airing cupboard it will have got warmer than normal, plastic and heat. With the other problems of the system it may have been "pumping over" meaning the whole tank eventually gets up to primary or at least the same temp as the stored hot water (60C+). Plastic tanks are not designed for that...

A few tens of pounds, replace the bit of ply at the same time. Plastic tanks need support over their entire base area. Probably worth using new tank connectors for the feed and overflow pipes, a new ball valve is only a few quid as well.

Yes a tank is a tank.

[Mike Dodd]

Yes, feed, overflow and the outlet to the cylinder.

Of particular interest is that with an empty F&E (she turned the inline valve off when she found the leak), I added a small amount of water and the leak *appeared* to start immediately - although this could possibly be due to the weight of the tank squeezing water from the plywood - I simply don't know.

I'm tempted to move the tank into the attic - a few quid for some copper pipe is worth it for the ease with which I could replumb this rather than work in such a tight-squeeze area.