Overflowing from Cold Water Storage Tank

[zayd]

I know that this problem has been done before and I have scoured all the posts but neither I or my plumber can find the solution.

I recently bought my first house and had the bathroom refitted. In doing this I had a new bathroom suite installed including a basin mixer and a 3 way thermostatic bath/shower mixer with a concealed valve. As I understand both of these devices have non return valves fitted to them internally. The kitchen mixer tap is older but I have seen that both the hot and cold pipes have non return valves fitted. I also had a single feed shower pump fitted to the hot water service pipe attached to the cylinder.

My hot water system is indirect with a CWST in the loft, sitting lower beside this is the F+E tank. All the bathroom cold taps are supplied from the cold water mains. The CWST has only one inlet from the cold mains at the ball valve, which has recently been replaced to the part 2 version. There is one outlet that supplies the hot water cylinder.

The problem I am having since the installation of the bathroom is overflowing from the CWST, through the pipe into my back garden. The F+E tank is not overflowing at all. I have shut the mains water into the CWST and shut off the outlet valve. After an hour I found that the tank had almost filled up with warm water which was coming out the expansion pipe that hung over the tank. This overflowing was occurring before I fitted the shower pump.

Other diagnostics I have carried out included; isolating the hot water services by shutting off the valve on the shower pump. If I am not mistaken would this not rule out any faulty mixer taps inside the house. The overflowing still continued after this action. Only after shutting the mains cold water in the street did the overflowing actually stop.

I do have unbalanced pressure at my shower mixer and I was going to fit a pressure eqalising valve to the supply pipes, but I can't see how the cold feed could push past the non return valve and backfeed into the cylinder. Especially when I have isolated the hot services valve on the shower pump hose.

All I know is that some how the cold water pressure is pushing the hot services causing this overflowing.

Thank you for reading this long post.

 

[Homesafe]

I know that this problem has been done before and I have scoured all the posts but neither I or my plumber can find the solution.

I recently bought my first house and had the bathroom refitted. In doing this I had a new bathroom suite installed including a basin mixer and a 3 way thermostatic bath/shower mixer with a concealed valve. As I understand both of these devices have non return valves fitted to them internally. The kitchen mixer tap is older but I have seen that both the hot and cold pipes have non return valves fitted. I also had a single feed shower pump fitted to the hot water service pipe attached to the cylinder.

My hot water system is indirect with a CWST in the loft, sitting lower beside this is the F+E tank. All the bathroom cold taps are supplied from the cold water mains. The CWST has only one inlet from the cold mains at the ball valve, which has recently been replaced to the part 2 version. There is one outlet that supplies the hot water cylinder.

The problem I am having since the installation of the bathroom is overflowing from the CWST, through the pipe into my back garden. The F+E tank is not overflowing at all. I have shut the mains water into the CWST and shut off the outlet valve. After an hour I found that the tank had almost filled up with warm water which was coming out the expansion pipe that hung over the tank. This overflowing was occurring before I fitted the shower pump.

Other diagnostics I have carried out included; isolating the hot water services by shutting off the valve on the shower pump. If I am not mistaken would this not rule out any faulty mixer taps inside the house. The overflowing still continued after this action. Only after shutting the mains cold water in the street did the overflowing actually stop.

I do have unbalanced pressure at my shower mixer, but I can't see how the cold feed could push past the non return valve and backfeed into the cylinder, whilst the valve on the shower pump hose is off.

All I know is that some how the cold water pressure is pushing the hot services causing this overflowing.

Thank you for reading this long post.

how do you know these are non return valves, and not just plain service valves?

 

[zayd]

Now that you mention it, maybe I have mistaken the ones in the kitchen as just service valves. It's just that there are already service valves above the ones I mentioned that have levers.

 

[Agile]

Most of those valves are really designed for low pressure ( tank fed ) supplies and are not to be trusted for mains water pressure on one side and LP on the other.

Its useless to have unbalanced pressures as that cannot give any chance of setting shower temperatures properly.

You seem to have a pretty nupty plumber!

Tony

 

[Homesafe]

either your showers are letting cold pass to hot side or you have a dodgy cylinder prob.

 

[tamz]

Only after shutting the mains cold water in the street did the overflowing actually stop

You've answered your question here. Think about it.

 

[Homesafe]

Only after shutting the mains cold water in the street did the overflowing actually stop

You've answered your question here. Think about it.

you sound like a shrink.

 

[tamz]

wi ma head in a sink

Pretty obvious answer to the op's question is straight in front of him.
Most British systems still in use are not designed for high pressure.

 

[zayd]

After many hours of deducing I think the problem may be with my kitchen sink mixer. I say this as I have a stop valve to the mains cold water in the bathroom, which after isolating does not stop the overflow.

 

[tamz]

Well done sherlock

 

[Homesafe]

your sherlock tamz! he's watson.

 

[zayd]

Hello people I'm back with more woes.

After isolating the kitchen mixer feeds the overflowing did not stop. What I did however observe, is that the gravity feed outlet from the CWST is backfeeding with hot water.

Does this outlet go straight to the boiler to supply it with water for heating. And if so then could the problem lie with my boiler and a valve that is not working properly, thus allowing hot water in the boiler to return to the CWST in the loft.

 

[jacobball]

have you got 2 tanks in your loft, a smaller one and a bigger one? if so is the smaller one higher than the bigger one??

 

[Goldspoon]

He already stated...

My hot water system is indirect with a CWST in the loft, sitting lower beside this is the F+E tank

 

[Goldspoon]

I would suggest that, as some have already suggested, mains pressure is dominating a mixer tap or mixer shower and pushing the hot back into the hw cylinder and up and into the large loft tank (CWSC).

You can verify this by putting a 22mm gate valve on the hot water pipe after it leaves the cylinder (make sure it is AFTER the vent). Switch gate valve to off and see if this solves problem.