Cold water storage tank overflow

[Bald Eagle]

Hi, I wonder if you could help me. The overflow pipe drips intermittently from the large cold water storage tank in the loft. Not the small F and E tank. The ball valve has been checked and is working ok. The vent pipe from the hot water cylinder is not venting any water into the tank, and the water levels in both tanks are at the same level, which leaves me to believe the only way the tank is filling is by the cold-water storage tank feed pipe from the copper hot water cylinder. This is a gravity fed hot water system from a Rayburn back boiler flow and return to the coil in the cylinder along with a backup emersion heater. Could a blockage or a faulty coil be the cause? There are no mixer taps in the plumbing system, and the system has never been flushed. I have found some build-up of pipe corrosion due to a slightly low ph in the water. I built the house 23 years ago. So, my real question, is there a conclusive way to determine if it’s the hot water cylinder heating coil, the cylinder, a blockage, or all three, before I rip out the lot at great expense?

Thanks for taking the time to read hopefully respond.

 

[Chuck]

Do you have any devices (mixer taps, showers, etc.) that could conceivably pass mains-pressure water across to the domestic HW and (indirect) CW pipework? If not, a faulty float valve is much more likely to be the problem than any of the more exotic things you have in mind, particularly if the problem is intermittent. I wouldn't trust anything short of replacement to prove a float valve suspected of intermittent leaking is 'working okay'.

Can you say more about "the water levels in both tanks are at the same level,", please? The level in the F/E tank should go up and down depending on the average temperature of the water in the heating system. Do you mean that they are both at the same height above ground, so the F/E is propped up on something? How far below the overflow outlet is the CW tank's normal level? Consider posting a diagram showing the levels.

Meanwhile, you could try tying up the CW store float valve arm and then run a cold bath to half-empty the tank. Monitor the height in the F/E tank for the next couple of hours and see if it falls at all when the CW tank level is reduced. Use a plumb line supported by a lath across the F/E tank so you can resolve small changes in its level.

 

[Bald Eagle]

Do you have any devices (mixer taps, showers, etc.) that could conceivably pass mains-pressure water across to the domestic HW and (indirect) CW pipework? If not, a faulty float valve is much more likely to be the problem than any of the more exotic things you have in mind, particularly if the problem is intermittent. I wouldn't trust anything short of replacement to prove a float valve suspected of intermittent leaking is 'working okay'.

Can you say more about "the water levels in both tanks are at the same level,", please? The level in the F/E tank should go up and down depending on the average temperature of the water in the heating system. Do you mean that they are both at the same height above ground, so the F/E is propped up on something? How far below the overflow outlet is the CW tank's normal level? Consider posting a diagram showing the levels.

Meanwhile, you could try tying up the CW store float valve arm and then run a cold bath to half-empty the tank. Monitor the height in the F/E tank for the next couple of hours and see if it falls at all when the CW tank level is reduced. Use a plumb line supported by a lath across the F/E tank so you can resolve small changes in its level.

Do you have any devices (mixer taps, showers, etc.) that could conceivably pass mains-pressure water across to the domestic HW and (indirect) CW pipework? If not, a faulty float valve is much more likely to be the problem than any of the more exotic things you have in mind, particularly if the problem is intermittent. I wouldn't trust anything short of replacement to prove a float valve suspected of intermittent leaking is 'working okay'.

Can you say more about "the water levels in both tanks are at the same level,", please? The level in the F/E tank should go up and down depending on the average temperature of the water in the heating system. Do you mean that they are both at the same height above ground, so the F/E is propped up on something? How far below the overflow outlet is the CW tank's normal level? Consider posting a diagram showing the levels.

Meanwhile, you could try tying up the CW store float valve arm and then run a cold bath to half-empty the tank.Monitor the height in the F/E tank for the next couple of hours and see if it falls at all when the CW tank level is reduced. Use a plumb line supported by a lath across the F/E tank so you can resolve small changes in its level.

 

[Bald Eagle]

To Chuck (Esteemed)I don't think my reply's are getting sent so I will try again.
Thanks Chuck, no mixer taps in the plumbing system, not sure about the shower which is a Trevi Therm MK1 built in thermostatic shower valve (cold main in /hot in from cylinder). New ball valve and float fitted. Yes, I raised the F and E tank so that the water levels are the same. The water level in the C/W tank is about 25mm below the overflow outlet. Sorry Chuck little confused about tying up the CW store float arm and running a cold bath to half empty the tank, the cold is from the main, do you mean the hot to empty the tank? if so I will then try your next tip to monitor the F/E tank

 

[Chuck]

not sure about the shower which is a Trevi Therm MK1 built in thermostatic shower valve (cold main in /hot in from cylinder).

Okay, so this shower is a potential route for direct (mains pressure) cold water to back-fill the indirect system and raise the level in the CW store.

Yes, I raised the F and E tank so that the water levels are the same.

Why?

The water level in the C/W tank is about 25mm below the overflow outlet.

Okay in theory but in practice I'd allow at least 50mm because float valves don't cut off sharply and I've encountered a couple of cases where wind in a particular direction blows into the overflow causing ripples on the tank surface that disturb things enough to cause overflowing.

Sorry Chuck little confused about tying up the CW store float arm and running a cold bath to half empty the tank, the cold is from the main, do you mean the hot to empty the tank? if so I will then try your next tip to monitor the F/E tank

Okay, it's unusual to feed a bath from the direct supply but if that's really the case and the CW store only supplies the hot cylinder just tie up the float valve and wait for someone to have a (warm) bath.