Suspected airlock in shower pump

[catesr]

I have just had a new shower installed. It works fine when you want cold water (not often), but when you turn up the temperature to warm/hot, the pressure drops massively and it's like standing under a watering can.

The shower is a Grohe thermostatic valve. The pump is a 3 bar twin impeller pump. The cold feed is from a tank in the loft. The HWC is at first floor level, with the pump at the base of the cylinder. A Surrey flange is fitted to the HWC, which feeds the pump via 22mm pipework. Pipework between pump and shower is 22mm for about 500mm, then down to 15mm poly pipe for the remaining 6 metres. The poly pipe goes directly up into the loft (2 metres), then across 3 metres, then down 1 metre to the shower valve.

I have bled the water through for around 10 minutes with the pump off and this seems to get rid of a lot of air. When you turn the pump back on, the pressure when hot is acceptable (but not really powerful). However when left overnight, the air returns into the system and the hot water pressure drops again dramatically.

My plumber has no idea what the problem is. He has checked that the pipes are the right way around and that the HWC is not corroded inside.

Any ideas please, because at the moment I have a new and expensive bathroom, with a pretty useless shower which only works if I bleed the system through every day.

Thanks

Rod

 

[leakydave]

Have air vents been fitted in the highest point of the pipework after the pump? This should get all the air out and give you a decent shower... most manufacturers recommend the fitting of vents at the highest point... refer to pump manufacturers instructions.

 

[catesr]

No they haven't - how do they work ? Surely if I have bled the system through and know there is no air in there and then the pump and the shower are both off - how can air be introduced into the system again ?

 

[leakydave]

its hard to bleed air downwards, it floats. Air vents will cure your problem once and for all. Isolate supplies, drain, fit thumb vents at highest point, fill, vent and enjoy the shower... what sort of plumber did you have?

 

[catesr]

OK, thanks - I'll talk to my plumber about this idea. What about fitting a non-return valve to the hot output pipe from the pump - would this stop air entering back into the pump from the shower ?

 

[catesr]

Maybe some more (hot off the press) information may help too. In another bathroom, we have just had a new bath fitted which is fed by the same HWC (unpumped). Flow rate with the old bath taps was fine, but hot water flow rate with new (monoblock) tap is awful - I guess it will take around 15 minutes to fill the bath. The plumber has just connected the new tap to the original pipework though.

I notice that the flexible steel-braided pipes to the new monoblock tap are quite narrow. Question - how does pipe diameter affect flow rate - would you expect to see a dramatically reduced flow when swapping from a 22mm pipe fed tap to this flexible pipe fed monoblock tap ?

Reading some of the other posts on this site, I can see two options...
1. Raise the level of my HWC by a couple of feet to increase flow
2. Feed the bath via the existing 3 bar pump I have

Advice would be appreciated.

Thanks

Rod

 

[leakydave]

you will need to be careful feeding the bath with the pump. If you turn hot on only, the pump will still be pumping cold, even though it isn't going anywhere. You can get a pump designed for this purpose with a bypass valve inside. Read the information that came with your pump..

 

[catesr]

Can anyone recommend a good quality plumber in the Welwyn area of Herts ?