Mira shower valve letting by on unvented system

[Pete H]

Hi to all any advice on this please,
Fitted mira shower valve, inset bir, approx 3 months ago. This replaced old built in valve which worked ok but was looking a tad tired.
Valve has started to let by only when water heating comes on in morning and evening. Hot water system is unvented, tank in loft, megaflow.
Would assume that seals have blown in shower valve, surprised considering M.I.s state stactic pressure 10bar and operating pressure up to 5bar , but to prevent happening again should i be fitting a prv and a mini expansion vessel on the hot feed to shower valve only. All other outlets in house are ok including bath mixer shower.

Any advice most welcome

cheers

Pete H

 

[Simon F]

Valve has started to let by only when water heating comes on in morning and evening. Hot water system is unvented, tank in loft, megaflow.

what pressure is the water getting up to when heated?
sounds like the expansion air bubble has been lost or depleted

 

[jtsplumbing]

Had this at home with a mira running off a combi, Fitted PRV on cold main no more problems.

 

[Pete H]

Hi guys thanks for this, will have to get back to customer carry out some checks. Cold feed to cylinder has prv but will check this and pressure and if expansion air bubble has been lost.

Cheers

Pete