Hot water in cold water storage tank....

[MarkH]

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!!

 

[Kings]

Does the level of the tanks go up? This would confirm mains water entering the HW system.

My only other thoughts are you are getting a flow between the CWST due to a blockage or a high level of demand on one tank. Before the level can be replenished it is also sucking water out of the other tank and up from the other HWC.

Or that connecting pipe is blocked and the higher level of one tank is causing water to flow round.

It's a confusing one - why do you need 2 tanks anyway? The other thing to consider is to separate the systems.

Last question - is the power shower on at any time to be the cause of this problem? I'm assuming it draws from one CWST and the HW which is fed by both tanks, I'm wondering if this is causing a flow between tanks.

 

[MarkH]

Does the level of the tanks go up? This would confirm mains water entering the HW system.

My only other thoughts are you are getting a flow between the CWST due to a blockage or a high level of demand on one tank. Before the level can be replenished it is also sucking water out of the other tank and up from the other HWC.

Or that connecting pipe is blocked and the higher level of one tank is causing water to flow round.

I am fairly sure I have made sure both CWST and HWC are full then switched the hot water on - still happens - which would suggest that there was no blockage...? But I do understand what you are saying about having a higher level of demand on one tank....

It's a confusing one - why do you need 2 tanks anyway? The other thing to consider is to separate the systems.

We have two showers fed from one pump (a large pump) and would empty a single tank in a few minutes - so we had a second tank etc installed.

Last question - is the power shower on at any time to be the cause of this problem? I'm assuming it draws from one CWST and the HW which is fed by both tanks, I'm wondering if this is causing a flow between tanks.

I see what you are saying...

However the shower is only used in the morning - this happens all the time the hot water is on.

 

[Deleted member 2053]

I think you may find that this is nothing more mysterious than convection. draw out the pipework layout and then consider what would happen if one HWC is full of hot water and the other only half full. The water in the second tank will on average have a greater mass and movement may well ensue. Dependant of course on how the things are coupled.

 

[MarkH]

I think you may find that this is nothing more mysterious than convection. draw out the pipework layout and then consider what would happen if one HWC is full of hot water and the other only half full. The water in the second tank will on average have a greater mass and movement may well ensue. Dependant of course on how the things are coupled.

I agree - a case of gravity circulation.

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?

 

[MarkH]

Changed the cold water feeds coming out of CWST's so that both HWC's are fed from one CWST - breaks the circuit.

Problem solved !!!! 😀

Thanks to those that replied.

 

[dam]

Just for ref which CWST did you take from!

 

[MarkH]

I agree - a case of gravity circulation.

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?

Correction to the above :

Draw to shower from CWST 2

Just for ref which CWST did you take from!

Capped off CWST 2 and feed HWC from CWST 1

Not ideal, as I would have preferred the shower and HWC feed to be the other way around. We use the shower every day without fail so little chance of stagnant water.

However, as all this was done by BG as part of the Homecare insurance I wasn't going to complain. I am going to replace both tanks with one big one next year - a neater solution and zero chance of stagnant water.