Bristan 1901 shower dripping

[richardindorset]

Had a dripping Bristan 1901 shower mixer that stripped its threads on the on/off flow control, so bought a complete new valve. Fitted it but I'm getting a slow drip when off. Cranking more on the on/off flow control makes no difference.

Just for a test, I took out the thermostat module and spring. The on/off flow control works perfectly, no need to use any pressure on the handle. No drips.

Could the new valve be faulty?

Obviously the spring in the thermostat module is pushing against the whole valve unit, basically forcing it open. As you close the valve it has to compress that spring. Just wondering if the pring pressure is making the valve body go slightly out of square o the o-ring doesn't seal.

Any ideas?

 

[CountryFan]

Could be the valve seating?

 

[richardindorset]

Could be the valve seating?

Initially I thought this too, but I've removed all traces of limescale and debris from the housing. The valve closes perfectly if the thermostat sping is removed.

 

[CountryFan]

Not entirely sure then. Maybe speak to Bristan?

 

[richardindorset]

Not entirely sure then. Maybe speak to Bristan?

Yeah, sent them an email. It's odd and annoying!
There are two springs in the thermostat module, I'm wondering if there is some sort of spring pressure balance that is slightly out with the old housing and new valve.