Shower air lock

[sscott1]

Hi,
Can anyone help.
Changed shower pump with same replacement twin positive head 1.5 bar and changed shower mixer/head etc. Having sucked through the hose the pump starts and runs ok. No issue unless shower not used for say 4/5 hrs then shower will not start without sucking through again.
Hot supply is from the cylinder downstairs and cold from tank in loft sitting on joists. Cold water head from base of tank to shower head about 400mm. As stated plumbing is unchanged from before - same pump spec and head of cold water.
Sower valve suitable for high and low pressure systems so I am now at a loss why the water has to be sucked through all the time after not bei g used for a while....

 

[Aquazone]

When the water comes through the shower, are you letting it run off all the air in the pipe run before shutting it off?
How is the hot water fed from the hot water tank? Does it have its own tapping?
Have you a drencher type shower head? Changing this or the shower mixer valve may have caused a bit more resistance on the run, and you might not have enough flow through the pump to activate the flow switches?
Is anything else attached to the pump - bath tap etc?

 

[sscott1]

Many thanks for your reply.
Regarding your questions:
1. Ran shower and then used twice in succession. Ran with shower head detached and hose lying in bath.
2. Hot from hot water tank - unable to determine if one of the tappings is the shower feed. Tank is downstairs next to boiler and shower is upstairs in main bathroom.
3. Shower head is one of the 6 mode from Wickes and new shower valve was supposed to be all system compatible.
3. Nothing else connected to pump.

Re-calibrated shower valve as when it did work could not get completely cold only warm...
This has now fixed this temp issue, could this cause any flow restriction??
Will monitor next couple of days - works at the moment. Thanks again.
Stuart

 

[sscott1]

Many thanks for your reply.
Regarding your questions:
1. Ran shower and then used twice in succession. Ran with shower head detached and hose lying in bath.
2. Hot from hot water tank - unable to determine if one of the tappings is the shower feed. Tank is downstairs next to boiler and shower is upstairs in main bathroom.
3. Shower head is one of the 6 mode from Wickes and new shower valve was supposed to be all system compatible.
3. Nothing else connected to pump.

Re-calibrated shower valve as when it did work could not get completely cold only warm...
This has now fixed this temp issue, could this cause any flow restriction??
Will monitor next couple of days - works at the moment. Thanks again.
Stuart

 

[pmuzz63]

Is it a positive head pump? If so, there is probably insufficient flow to start the pump (activated by a flow switch). With only 400mm head, you really need a negative head pump (with a tiny pressure vessel on it). Fingers that, you can get pump starter switches which temporarily override the flow switch when you press them. This kick starts the pump which has will then remain on until the shower valve is closed.

 

[pmuzz63]

Failing that (not fingers that!). I hate predictive text!

 

[sscott1]

Cheers, negative head pump it is then.....

 

[PlumbBobBob]

where is the pump in relation to the cylinder?

 

[sscott1]

Hi,
Cylinder on ground floor - pump up 1 floor level

 

[Shower Engineer]

Check hot water connection to cylinder, make sure it is air free. Sounds like air from cylinder entering pipework to shower pump.