Bath/Shower mixer problem

[Goudurix]

I have a bath / shower mixer tap - the type with a pull up diverter between the taps, the diverter stays in whichever position you select (i.e. does not need water pressure to keep it up).

The system is 'traditional' gravity fed - the cold water is supplied to shower only from the loft tank. All other cold water outlets (taps / toilets) are mains.

Recently the mix of water in the ensuite has become unbearably hot - there has been no change to the hot water temperature setting.

I have removed the tap glands and diverter there does not appear to be any blockage the seals look in good condition - I even replaced the glands, I have had descaler in the tap (although we are soft water area and scale is not a problem elsewhere!) The shut off valves for the feeds are both fully open.

The house bathroom has a similar tap - which has a separate cold water feed from the tank in the loft - but this is working fine -so cold water tank is fine (physical check confirms level in tank ok) .

It seems to be a pressure problem - as the temperature reduces as I lower the shower head - but I don't understand why this may may be - it has worked fine for 2 years since I replaced the tap unit because of a failed diverter!!

I have run the water through the unit with the glands removed in case there was a blockage.

Any thoughts / ideas what I can check / do next?

Thanks

[harry]

So what happens when you turn the hot tap on the mixer completely off? No water at all?

[Eric]

Cold tank not filling up as fast as it empties.

[Goudurix]

Tank appears to fill ok - house shower works fine

When hot tap is off the cold water flows fine. Without some sort of meter / guage it is difficult to check pressure in the two feeds. But if I remove shower head and point the hose upwards, both hot and cold jets on their own appear to rise to the same height (but obviously this is just a visual estimate!)

Feed is 22mm to both hot and cold

Nothing wrong with the design - it has been fine up to now

Only thing I can think of is debris from the tank settled in the pipe and reducing flow in the cold feed - any ideas how I could 'blow' this through?

[bert]

In message , Goudurix writes

Back flush with mains pressure using hose from another tap.

[harry]

Use a hosepipe connected to a mains pressure tap. Hold it against the bath taps, wrap a bit of rag round and force mains water in the "wrong" way. You will need assistance. Open low pressure taps first and close last or you will get wet.

I wonder if there is a washer problem? Airlock?

[Tim Lamb]

Not been following this thread but found Harry's suggestion to work in a holiday bungalow where the over winter drain down invariably caused air locking problems on re-use.

[Goudurix]

Washers are all new - came with new glands.

I will try the back flush technique when I get a day off!

Thanks for the help