Thermostatic shower valve problem.

[chapcot]

I have a real problem with a thermostatic shower bar which refuses to stop dripping. I replaced the washer in the on/off valve but still the drip. I then replaced the complete valve assembly but again no cure for the drip. I therefore assumed there must be damage to the valve seat so spent £125 on a new Aqualisa thermostatic shower bar. Just fitted it and unbelievably there is still a drip even with the the tap turned hard off. All I can think of is that the water pressure is too high and is forcing the valve back open slightly - is this possible? The house has a mains pressure water system with an unvented hot tank.
Any help or advice would much appreciated.

 

[terryplumb]

where exactly is it dripping ?can u post a picture ?

 

[chapcot]

Thanks for coming back so quickly. Drip is from the shower head. In other words water is leaking through the valve then via the hose to the shower head. The drip is quite slight,probably only one or two drips per minute but enough to splash onto shower enclosure/tiles and give a lime scale build-up after a few days as this is a very hard water area. Not sure if a photo would be much help as all it would show would be a drip at the shower head.

 

[terryplumb]

OK ,a few things some valves are made for low pressure plumbing systems ,check what yours is and what maximum pressure it's designed to cope with. you mentioned that you have taken something apart and changed a washer, is it within the horizontal mixer ? short term fix if you have isolators on the pipework just before the valve is to turn them off

 

[chapcot]

Checked the specs of the unit and it says "suitable for unvented systems and designed to control static pressure up to 10 bar but where pressure is likely to exceed 5 bar, a PRV must be fitted to the incoming mains". Judging by the force of the cold water tap I suspect it may be above 5 bar at times so have ordered a gauge to check and will post result. Have been using isolator valves as you suggest but its a pain having turn off/on for every shower.

 

[terryplumb]

I am sure it would be a pain in the u know where !!! how about my question about the changed washer ,in the valve ?? original or second valve ??

 

[picasso]

What type of unvented cylinder ? megaflo ect