unvented hot water cylinder

6 Apr 2008
Reaction score
United Kingdom
have a problem with the unvented hot water cylinder on system, problem being is it does not produce enough hot water, the cylinder has 2 emersion heaters on it also flow and return to boiler and flow and return for heating, it also has a pump at back of cylinder which i guess is for a higher flow rate. the tank is hot and so are the pipes but when you turn tap on you only get a hand full of hot water then goes cold any suggestions would be great help the system is about 16 years old it also has flow switch on pipe work which has been renewed, its baffling seems to have small pockets of hot water in tank.
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Perhaps the pump at the back of the cylinder is a bronze secondary circulator and it has packed up working.
sounds like a mixing valve problem is there a valve after the hot water comes out of cylinder if so is the pipe between hot?
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is it possible you have a thermal store, not unvented?
BG engineers used to get them mixed up all the time :LOL: :LOL:
This will be something like a thermal store and the plate HEX is only warming itself up from the latent heat of the store. You will get about a litre of hot water and thereafter cold.

Either the pump has failed or you need another flow switch.

This is very unusual because this forum's most prolific and opinionated correspondent maintains thermal stores are the most reliable source of hot water available.

Some others here disagree, but we are all charlatans who just go around repairing them.
I would also guess that its a thermal store and there is a blending valve which has failed as they usually do after a few years.

They are not very reliable and can get badly sludged up and leak around the seams near the bottom.

Other types with a plate HE seem to easilt get blocked with lime scale because the store temperature is run too high.

A photo would help us to be sure!

Dr Drivel stays clear when anyone posts about a failed thermal store because:-

1. He always says they are very reliable.

2. He cannot diagnose faults.

3. He cannot repair anything even if he knew what was wrong.

4. His brochures dont include servicing or repairs.
If I am right, this is a thread about unvented cylinder. Where is BB.
Its not very clear exactly what it is Danny!

The clue about having a "flow for the heating" makes us think that its probably a thermal store.

It would still be a cue for BB but as I have said above he will be staying away as its failed and according to him they are ultra reliable!
the flow switch has been replaced, forgive me if im not very clear as its a friend in need, i am not experienced on plumbing side of things but i know enough to get round, shall try posting picture up probably at weekend thanks again for all the help

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