Shower Mixer valve flow pulsing

[lidster]

Bought and fitted this concealed Thermostatic Shower Mixer Valve.

https://www.amazon.co.uk/gp/product/B07C1QJ839

Has been working really well for 6 months. now it pulses. Gravity fed system. no pump. 22mm dedicated cold from header tank, 22mm hot , both reducing to 15mm for the last metre.

It flows well for 1 minute, then pulses. this video shows it better than i can explain.

https://photos.app.goo.gl/RiWkXs8KdDTtGfyH7

Can anyone advise how to fix please?

 

[HERTS P&D]

Have you checked the float valve in the loft is working correctly?

Andy

 

[Madrab]

After checking the levels in the cistern in the loft I'd be looking at the non return valves or thermostat, more probably the later. Is anything else pulsing? Taps etc?

 

[lidster]

After checking the levels in the cistern in the loft I'd be looking at the non return valves or thermostat, more probably the later. Is anything else pulsing? Taps etc?

thanks for the replies....

Nothing else pulses - downstairs hot tap (dual flow mixer) no probs at all. The CW tank is full and looks to be filling up as quick as it can from raising main. Both the hot and cold fly out at the bath taps and empty the loft and HWC rapidly. The bath has its own dedicated cold feed as well - so not on the same shower run.

Are the NRV's the accessible screw nuts from the front of the valve? https://www.amazon.co.uk/gp/product/B07C1QJ839
if so - ill give it a go at replacing.... if the manufacturer ever get back to me. Or can someone recommend decent NRVs?

 

[lidster]

After checking the levels in the cistern in the loft I'd be looking at the non return valves or thermostat, more probably the later. Is anything else pulsing? Taps etc?

cheers madrab - if its the thermostat does that mean total replacment to fix? It runs for 30 - 60 secs fine - then starts pulsing. With the shower fully on - ive gone back to the airing cupboard and isolated the cold feed to the shower and it stops the shower altogether. so the scald protection part is working. fully on hot (past the safety trigger) it still pulses. fully on cold - trickles out.

 

[Madrab]

Hmmmm .... it sounding more and more like the thermostat is the cause I'm afraid. It may need cleaned, some have a filter mesh. if you know the make then you may be able to replace the thermostat rather than replace the shower but some of them are so expensive it's sometimes cheaper to replace the whole thing.

 

[lidster]

Hmmmm .... it sounding more and more like the thermostat is the cause I'm afraid. It may need cleaned, some have a filter mesh. if you know the make then you may be able to replace the thermostat rather than replace the shower but some of them are so expensive it's sometimes cheaper to replace the whole thing.

Yep think you're right. Turned on fully hot and it flows ok. As soon as I try and mix a little cold in it the flow pulses. This valve allegedly comes with a 10year guarantee. Hoping to get the parts.....