Shower Positive/Negative head

[Robinb]

I have a shower with a pump (positive head) for both hot and cold supply. Although the shower head is positive, the pipes from the pump are routed upwards into the loft across the ceiling and down to the shower.
In the summer with the central heating off it works fine. In the winter with the heating on I have trouble starting the hot water flow (cold is ok) although the pump starts ok. I have to run the shower every day for a few minutes with the shower head on the tray. If I go on holiday when I get back the hot water will not start. I have to turn off the water, remove the nut from the pump on the hot water side and turn on the supply until water comes through and replace the nut!
Will a negative head pump solve this problem?

 

[seco services]

how is the hot connected to the cylinder ?

 

[Robinb]

With a flange (surrey type) I think.

 

[seco services]

have you a non return valve on the hot water outlet of the pump ?

 

[jameshunt]

as long as the pipes do not go higher than the water level then the pump should be ok ... as seco services said, maybe a check valve in the pump is sticking.... a lot of shower pumps and showers themselves do have check valves built in...

 

[seco services]

you mention the central heating side affecting it.
can't see how the heating is affecting it. not even hw only.
but you say its ok in the summer. but you'll still need to heat the cylinder in the summer.
if hw not affecting it then heating shouldn't.

 

[Robinb]

I do have a non-return value on the hot water side between the cylinder and the pump and another between the pump and the shower.
The pipes do not go higher than the water level in the top tank.
I do not see how having the central heating on could make a difference but mentioned it as there is a significant improvement in the summer.

 

[Boxerman]

I had a very similar situation and when I contacted Salamader tech support they said that as the pipes were routed through the loft and in my case travelled a fair distance >20m then I effectively had a negative head situation. I bougth their RCM3 negative head kits and it now works fine

 

[seco services]

you shouldn't have a non return on the hot between the pump and cylinder.
the pump needs to vent back to the cylinder with a non return valve their it can't.

remove that one first and try it.

 

[Robinb]

That was added in an attempt to cure the problem. Initially there were no non-return values and the problem existed.

 

[seco services]

have you any pics of the set up ?
how long the run is from pump to shower
what pump it is etc

 

[Robinb]

I do not have any pics but could take some if required.
The pipes are 1.4m up from the pump into the loft, 2m across the loft and 0.6m down to the shower head making 4m in total.
The pump is a heavy duty brass shower pump from Newteam Ltd rated at 3 bar.