Cold water feed tank is hot?

19 Mar 2011
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United Kingdom

Just moved to a new flat and sadly found a problem with the boiler which I hadn't noticed on initial inspection.

The system is an electric PulsaCoil 2000 hot water boiler - a large cuboid steel box, which I assume contains a hot water tank and immersion heater etc. Haven't taken the front off yet, but might investigate.

On a shelf above is a small plastic tank, with pipes running into the boiler - I assume a cold water feed tank to keep a head of water for the boiler.

However I have noticed that this cold water tank was boiling hot, and has developed a leak from one of the pipe connections. I assume the heat has expanded the tank or the connections and allowed the leak.

Any suggestions as to what might be causing the header tank to be hot?

One possibility could be that I have unwittingly used the 'boost' heater for the last 36 hours non-stop. There are two wall mounted switches for the heaters, marked 'Heater 1' and 'Heater 2', so I switched heater 1 on, but subsequently noticed it also said 'Boost'. Perhaps I should be using the other switch?

However, I would expect the system to have some kind of cut-out and not vent hot water to the header tank under any circumstances.

Your thoughts are much appreciated!

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Could be the old mistake of the overflow fitted far too high up in the header tank, so that, if it fills right up to the overflow, water runs down the integral expansion pipe and the thing starts to thermo-syphon.

If so, the ball tap needs fixing, and the overflow putting in lower than the ball tap - as it should have been. However, that would really only apply to a set-up with an integral header tank. Otherwise, there may be an immersion heater thermostat stuck on or set dangerously close to boiling point.

Please get this checked, especially if it is a plastic cold water tank. They won't withstand boiling water for long.

Finally, you quite likely have some redress with the vendor of the property.
Hello mysteryman, thanks for your reply.

I've done some further investigation:

- The system is working normally, according to the indicator LED on the PSB that is blinking twice with a pause. The manual states this is 'normal operation'.

- The level of the water in the header tank was very high - up to the height of the open vent pipe, not over it, but certainly water must have been returning to the boiler via this pipe.

- The reason for the high water level was the ballcock allowing the water to rise too high before cutting out. This in turn was due to the deformation of the area around the water inlet pipe and ballcock valve - the bent plastic was allowing the whole ballcock mechanism to rise upwards, raising the water level.

- There is clear evidence of old water leakage in stains and marks around the cupboard where the boiler is located. There was also evidence of the previous residents putting newspaper down to soak up the water, and plastic pots to catch drips. This has clearly been going on for some time.

- The tank is full of some horrible looking residue, brown in colour. Clearly the system has not been serviced for some time. The water itself was clear.

- Both the ballcock inlet pipe, and the vent pipe, where they enter the header tank appear to be leaking very slightly, probably do to heat deformation of the plastic tank.

In the light of that lot I have taken the following actions:

- I have taken out some of the water from the tank, to bring the level below the vent pipe.

- I have turned the inline valve on the pipe supplying the ballcock valve off, to prevent the tank refilling again. I appreciate this is not a permanent solution.

I also plan to:

- Call a plumber and get the whole thing checked over.

- Possibly replace the tank, as the deformation means the ballcock can't be trusted even if adjusted for height.

- Contact the residents of the flat below to confirm any water leakage and if so, obtain confirmation that this problem occurred before I took ownership of the flat.

- Work out if I do have any redress with the vendor. Probably not, but it's worth a try.

Can you tell me what my investigations might mean for a diagnosis / fix?
Am I ok to leave the ballcock inlet turned off?
And would you have any further recommendations for things I should do or check?



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