Hot water in cold water storage tank....

[Mark_H]

This is driving me, and British Gas, crazy!!

I have a vented system with two hot water cylinders in the loft. A cold water storage tank sits above each one - they have a connecting pipe to ensure the water is level. Each CWST feeds a HWC, and also feeds the power shower. All other taps in the house are fed directly from the mains.

The problem is that hot water is going up the feed pipe into the CWST - which suggests that there must be mains pressure coming into the top of the tank. Now by my thinking, this can only be one of two things – cross over on mixer taps or a leak on the coil of the cylinder.

· All mixer taps have been checked for cross flow.
· Mixer taps downstairs are all suitable for mains pressure – the water doesn’t mix until it comes out of the tap.
· Taps upstairs have a pressure reduction valve fitted to 0.5 bar
· ALL taps have been isolated and this still happens.
· Both cylinders have been replaced over the last couple of weeks - initially BG suspected there was a leak on the coil and replaced one - didn't fix it. So the second was replaced as they thought it had a leak on the coil and the pressure was coming out of the top of that one and into the other one, pushing hot water up the feeder – still not fixed.
· New vent pipe fitted – thought that may be blocked.

Totally at a loss as to what the cause is - does anyone have an ideas or suggestions?

Thanks in advance for any assistance.

Mark

BG are coming out again tomorrow... the guy might as well move in, he has spent so much time here!!

 

[SurreyPlumb]

Do you have an old style washing machine with hot and cold feeds?

 

[Kristoflampie]

Thermostatic shower in the house?? Mains cold often crosses over past the poppet valves and pressurises hot tank, murder for unvented as it lifts the safety valves but vented would as you know just shoves hot out into the cold tank. Its a suggestion

 

[steved101]

could be the shower, although shouldn't really have a shower with unbalanced supplies...

so if your shower (manual or thermostatic) has cold mains, this could be the problem ..

 

[Mark_H]

Do you have an old style washing machine with hot and cold feeds?

Nope - cold water only.

Thermostatic shower in the house?? Mains cold often crosses over past the poppet valves and pressurises hot tank, murder for unvented as it lifts the safety valves but vented would as you know just shoves hot out into the cold tank. Its a suggestion

Shower is fed from the CWS - so balanced pressure.

Thanks for the replies - keep them coming!

 

[petit_pablo]

I had a mixer shower doing this a couple of weeks back. It appeared ok to the eye but put an isolation valve on it to check and the tank level remained constant.

 

[steved101]

if it was mains pressure (ie mixer tap/shower) forcing hot water into tank - then water would probably be coming from the overflow pipe also....

how would washing machine (hot and cold fill) affect this? (just curious)..

 

[steve32]

Turn off the cold feed valve on the opposite cylinder to the one getting hot and leave off for a few hours or all day and see if this stops the hot water going into the tank.
If it stops getting hot you have gravity circulation between the cylinders and roof tanks
If you have got gravity circulation you will need to alter the cold feed connections coming out of the roof tanks or as a last resort bring a 35mm supply from tank no 2 and tee of in 28mm to each cylinder, ballvalve in tank no 1 other cold connections from tank no 2 away from cylinder cold feed connections .

Hope this helps,

Steve

 

[seco services]

· All mixer taps have been checked for cross flow.
· Mixer taps downstairs are all suitable for mains pressure – the water doesn’t mix until it comes out of the tap.

still check the kitchen mixer as they are common for this when the bottom seal gos on the spout. then they can mix.

 

[steve32]

Further to my reply above i am assuming only one cold feed is getting hot if both are getting hot then the above won't apply.

 

[Mark_H]

Turn off the cold feed valve on the opposite cylinder to the one getting hot and leave off for a few hours or all day and see if this stops the hot water going into the tank.
If it stops getting hot you have gravity circulation between the cylinders and roof tanks
If you have got gravity circulation you will need to alter the cold feed connections coming out of the roof tanks or as a last resort bring a 35mm supply from tank no 2 and tee of in 28mm to each cylinder, ballvalve in tank no 1 other cold connections from tank no 2 away from cylinder cold feed connections .

Hope this helps,

Steve

I think you've got it!!

CWST 1 feeds HWC 1
CWST 2 feeds HWC 2

Ball valve on CWST 1 to refill
Draw to shower from CWST 1
Connection pipe between CWST 1 and CWST 2 to refill and ensure same level

CWST 2 is the one that gets hot!!

So would you just have another ballvalve on CWST 2. Cap off the connection between the two CWST's. But how would you draw from both to feed shower without causing the same problem?

Please spell out what you think needs doing - I am not a plumber!

Many thanks Mark

 

[steve32]

cold water entering tank 1 can go down cold feed to cylinder 1.
out of top cylinder 1 into top cylinder 2 up cold feed cylinder 2
into roof tank 2.
as the ball valve is on tank 1 cold water is heavier than hot it can create a circulation
cold water or air falls, warmer or hot water rises.
To check if this is the cause turn off cold feed to cylinder 1 as above.

 

[steve32]

if this is the cause you need to connect both cold feeds out of the same tank so the water temp is the same or as above with a 35mm bridge teeing to each cylinder.

 

[Mark_H]

if this is the cause you need to connect both cold feeds out of the same tank so the water temp is the same or as above with a 35mm bridge teeing to each cylinder.

Surely if I cap off the connection between the two CWST's therefore each one would be working independently and the circulation could no longer happen?

The only question would be that the power shower would then only draw from one CWST and I am concerned that there will not be sufficient water to supply.

I don't really understand "35mm bridge..." - I can't picture it and therefore not sure how it would help - sorry.

 

[steve32]

the connection between CWSTs is called a bridge you fit a 2nd out of the front of each tank connecting the 2 tanks in 35mm copper and then tee off in 28 to each clinnder
leave existing connection in place
Yes capping off the existing connecting between tanks will stop circulation
Depending on the size of pump you need min 50galls water for pump.
If it was my installation i would fit 1 large tank, shower pump connection opp end tank to ball valve.
if you cap off connection between tanks and fit ball valve in 2nd tank there is possibility of stagnant water in one tank subject to how connections are fitted and getting even pull on hw cylinders.
If you have tanks interlinked the ball valve should be on tank 1 outlets tank 2.
bridge between tanks one size larger tha draw offs.
If you connect (subject to water volume in tanks) both cylinders to tank 2 this may cure it.