Pumped shower fault any ideas?

[flyingsparks]

I have a mixer shower fed with a shower pump, twin impeller 2 bar. I have taken a new feed from cold water tank in 22mm to pump, changes to 15mm at pump.
Also fitted a warick flange to the hot water cylinder come out and down to the pump sited at floor level next to cylinder in 22mm and then changed to 15mm at pump.
The pump is a Screwfix flomaster
http://www.screwfix.com/p/flomasta-...ead-shower-pump-with-twin-impeller-2bar/32393

The shower is a wickes one.

Problem is pump will not start unless you turn shower to cold and then you can go back to warm. It also appears to always have air in the system, I think on the hot, when you first start it.
Is there a requirement for a check valves after the pump, or should they be built into the shower valve? Nothing is mention in the instructions?
The hot pipe comes out the warick flange and looking at it again ever so slightly rises by the looks of it before dropping down to the pump. Could this be where the air is coming from? Any ideas appreciated. Thanks.

 

[picasso]

Have you taken the vent off the lowest and the shower take off on the top of the flange ? you will also need a manual air vent at the highest point of the hot water pipework before it goes down to the pump.

 

[flyingsparks]

Yes got the shower supply of the top of the flange. Ah right didn't know about the manual vent. Do you think the very slight rise in the pipe (probably only about 5mm over 300mm ) could cause this problem too with the air?

 

[picasso]

I would have thought so.

 

[gigz]

Try turning the pump off and shower on, this sometimes clears the air without damaging the pump. Also check the filters (if fitted) to the shower are clear.