Hot Water/C/W supply overflow

[grekko]

Thanks in advance to to everyone for their advice/help, here's the situation now:
I still have the overflowing water from the cold water supply tank, and I've had a new float valve fitted, but the tank is continuing to fill and overflow(but not from the valve inlet).......the water in the tank is almost tepid at times. What has become noticeable is that the overflow will still run , even if it's only a trickle, hours after both the C/H and Hot Water is switched off at the boiler(cylinder thermostat checked and not faulty)......plus the hot water takes forever to get warm at the bathroom tap, much longer than previously.....there's also the problem of a reducing supply of hot water, it eventually runs to a trickle and I have to attach the washing machine hose to the hot tap to get a decent flow again (but that doesn't last for long after running the hot water).......had plumber/C/H engineer in and they are puzzled so you can imagine how worried I am becoming at this unsolveable? problem.......C'mon guys please please HELP!!!!!

p.s The central heating appears to be working fine with no problem getting radiators warmed up.

[plumbbob]

I still have the overflowing water from the cold water supply tank, and I've had a new float valve fitted, but the tank is continuing to fill and overflow

Which of the two tanks is overflowing? The larger or the smaller?

plus the hot water takes forever to get warm at the bathroom tap, much longer than previously

You mean the length of time it takes the hot water to reach the tap has increased?

I have to attach the washing machine hose to the hot tap to get a decent flow again

Explain what do you do with the washing machine hose and is this a new problem?

[grekko]

I still have the overflowing water from the cold water supply tank, and I've had a new float valve fitted, but the tank is continuing to fill and overflow

Which of the two tanks is overflowing? The larger or the smaller?

The larger CWS tank

plus the hot water takes forever to get warm at the bathroom tap, much longer than previously

You mean the length of time it takes the hot water to reach the tap has increased?

Exactly, a longer flow of cold water before hot arrives.

I have to attach the washing machine hose to the hot tap to get a decent flow again

Explain what do you do with the washing machine hose and is this a new problem?

I attach the cold water fill hose to the hot water fill connection and blow the hot water back,(taps closed of course) hot water can then flow from the taps, but the remedy has to be repeated every few days as the hot water flow reduces to a trickle..

[plumbbob]

[
The larger CWS tank

The most logical explanation is you have a faulty mixer tap somewhere. Either the bath, basin or kitchen tap. Have you had new taps fitted recently? I have had before where there is a hole between the hot and cold sides so when the taps are tyrned on water is forced up the hot. This can also happen on some mixer taps where the spout is too small and again cold is forced back up the hot side.

If the smaller central heating header tank water level is higher than the larger CWS tank, water from the heating circuit may be entering the DHW circuit.

Another thought, do you have a mixer shower?

[plumbbob]

It might explain why the hot water is cold too. The hot is being pushed back to the cylinder leaving the pipe filled with cold from the mains.

The airlock could be caused by-

1. An obstruction in the CWS cistern outlet restricting flow.
2, The gate valve between the cws cistern and the hot water cylinder is partially closed.
3. The cws cistern is running out of water allowing air to be drawn in to the feed.
4. You are not back filling with the washing machine hose long enough to expel all the trapped air.

[grekko]

Thanks guys for your quick responses, I'll have a shufty at each of the possible causes(shower mixer apart, haven't one) and let you know my results...... Merry Christmas to you all.