Gravity hot

[jmph]

Hi, i have a customer who has been having their part2 float valves in the loft changed every two years. I thought this excessive so did some investigating.
Have found that the bath shower mixer is on cold main and gravity hot. When customer put this on thw vent pipe let water into the tank. Has anyone ever put a non return valve on a gravity pipe? Its the only option i can see to stop the cold going back into the hot but im worried it will restrict the flow too much

 

[ShaunCorbs]

Yes on the bath pipe or switch the system to equal pressures eg unvented / pump

 

[oz-plumber]

I wouldn't put a non return valve on in this situation.
I would put a pressure reducing valve in the cold feed to the mixer - if possible

 

[Knappers]

Not a nrv on vent but could put one on hot feed to shower
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Or tank feed to cold side?

 

[Alan Wright]

1.0 Its illegal to put a non return valve on the vent pipe itself for obvious reasons.
2.0 You can put a non-return valve on the hot feed to a shower but if you do a 22mm single check valve is the one to go for (not a 15mm nrv or a double check)
3.0 You can boost the hot with a pump to overcome the mains pressure.

 

[jmph]

I wont be putting anything on the vent.
My reason for the nrv on hot is easiest and cheapest option. Customer wont want to get involved with pumps ans re directing pipes.