Ceiling has failed below water tank in loft

[Ben565]

Hi looking for a little advice here. About 6yrs ago I had the bathroom renovated complete with fancy Mira digital shower and bath filler. I have a gravity fed system so required the pumped version. So for this setup the hot water comes from the hot water cylinder, and the cold comes from the tank in the loft, but since the hot water cylinder is fed from the tank in the loft.. so effectively everything coming out of the shower or bath filler comes from the tank in the loft. Mira recommend a 230 litre tank. The bath filler runs at 16 litres per minute, and takes around 11 minutes to fill my bath so in theory 176 litres. The shower is less of an issue as it's only 12L/min and showers use less water than a bath anyway.

So the 230 litre tank was fitted in the loft, replacing the much smaller pre existing tank (which had been there for many years without any issues). I had my doubts at this point, it looked a big tank !

Last week the ceiling under which the tank sits came down, well partially anyway. There's been a crack there for a while with only the paper holding the plaster up, and recently noticed it getting worse. Could just be an old ceiling/plaster thats failed... could also be related to the 1/4 ton of water sitting on the rafters above it.

Had a look in the loft, it seems to be bowing under the tank alright !

The tank is sitting on a plywood base, with 3 bearers spread across 5 ceiling rafters. The ceiling rafters are only 4x1, not sure on spacing it's a 1920's house. The long end of the tank nearest the roof tiles is along a supporting wall, but the tank isn't actually sat on it. In the room below the tank is in the corner where the door is (the wall to the left of the picture/door is a floating wall)


To me this looks like the weight of the tank is bowing the ceiling rafters, bowing the ceiling below which has caused the plaster to crack off. Would you agree ?

Would you also agree this is a massive catastrophy waiting to happen? it's only going to get worse and ultimately the tank is going to break the rafters and the whole lot is going to come down.

Any suggestions for a solution to fix the issue? I thought of a couple:
Double up the ceiling rafters - They are only nailed to the roof rafters though so may just cause new problems
Fit deeper ceiling rafters - Same as above really, might make the rafters stronger but still only nailed to the same roof rafters.
Fit a smaller tank - Need to do the maths make sure the shower/bath filler pumps won't run dry

 

[Ben565]

*Edit they might be 4x2 ceiling rafters, not quite sure, probably, not very big anyway

 

[Wayners]

Tank should be on a platform that the wooden frame sits on internal brick walls

That lath and plaster ceiling is old so could be end of life, and other ceilings maybe ready to be pulled down or boarded over. look for Y shaped cracks and give them a push to test.

You can fit a strap across joists (wood) and get a couple of people to stand on it, fix to joists. When people step off ceiling may lift a bit.

 

[Ben565]

*Update the ceiling joists are 3x2, plywood base for the tank is around 20mm, and the bearers under the base ar 1.5 x 2.5 and lying on their side for some reason.

Also one of the ceiling joists isn't even touching the bearers it's just lower than the rest.