Hot water cylinder backfilling cold water storage

12 Aug 2004
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United Kingdom
:confused: Hi I am having a problem with my hot water cylinder. The problem is the water from the hot water cylinder is travelling back up the cold feed pipe causing the cold-water storage tank to overflow. I am certain that this is the problem as I have watched the vent pipe and the float valve but it still fills up .So the water can only be coming from the hot water cylinder.

I have tried draining the cylinder and starting from fresh but to no avail.

The cylinder is of the indirect type.
My central heating boiler is a gloworm wanderer model no 1648.

Any advice or help would be very much appreciated.
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is your f&e tank above your cold storage tank ?

if not your expansion pipe(the one that curls over the top) is blocked

if it is chances are the coil in the cylinder is punctured
Looks like new cylinder required or could be faulty mixer tap letting mains pressurise domestic hot water push up through cold feed, went to one yesterday.
PEDANTICVINDICTIVEMAN - I may be a bit late on this, being as the original post was in June but is there a simple test for the mixer-tap problem?

My loft tank that feeds the HW cylinder is also overflowing in the same way. If I sit and watch it I can see the wavy shadows of the hot water coming up through the cold feed in the bottom of the tank.

I checked the most obvious things: ball-cock, cylinder coil fracture, boiler stat, cylinder stat and all seem to be fine.

I have a mixer tap in the kitchen and a gravity-fed downstairs shower where mains cold could possibly be feeding back up the HW pipes into the cylinder - just not sure how to isolate whether it is this, or which one might be causing the problem.

Thanks in advance.
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If you have a gravity fed shower valve it wont be connected to the mains (or shouldn't be), it will have a low pressure cold supply from the same tank which feeds your hot water cylinder, if it didn't you would have uneqaul supplies to your shower valve making mixing difficult and could cause your syptoms, (did this problem arise at the same time the shower valve was fitted ?) the only way to check if it's a mixer tap to blame is to isolate the supplies to it, and see if it cures the problem, if there are no isolation valves on the pipes feeding the tap you could fit some, normally in line 15mm ballofix valves will do , good luck, let us all know.
It was the mixer shower as you suggested. I put the shower temperature on full-cold only and turned it on, then turned on a nearby mains cold tap and the shower pressure immediately dropped (I've since traced the pipework to confirm).

A final proof was that by leaving the mixer shower in the full-hot position when not in use (so cold input is off and hot input is full) the overflowing from the cistern stopped - as the cold was prevented from making its way back up the hot pipe. Not that this is a good permenent solution, so I've now fitted a tank-fed cold feed to the shower and all is well again.

The system had been incorrectly installed for >10 years but I recently replaced the mixer unit with a more modern one. Obviously the old solid brass job had just hidden the problem all that time.

So thanks for the help. Saved me a lot of hassle that tip. Hopefully someone else will benefit and can use this info too.

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