Airlock in cold feed to shower pump - gravity system

[grobsy]

Initial Plumbing set-up:
Loft: Cold water tank with 1x 22mm feed to HWC, and tee-ing off this 22mm just after it leaves the tank is a 15mm HEP feed down to the Cold side of the shower pump under the bath on ground floor. (there are no other Cold feed off the tanks as all the cold taps are mains pressure)
First Floor: Hotwater Cylinder with no special flange for shower pump hot.
Ground Floor: Bathroom with Shower pump underneath bath to supply mixer shower.

The above existing system was causing the shower pump to draw in air (no surprise) and make a bad noise intermittently.

I made the following change to sort this:
Fitted new dedicated Hot feed from Essex Flange in the side of the Hot Water Cylinder down to the Shower Pump under the bath. So the Shower Pump now has a dedicated hot & cold feed.

Problem now:
I managed to get the water to come through the h/c supplies and flow out of the shower head OK first time, but now after every 1 or 2 days an airlock develops in the shower pipes, particularly the cold, so when the shower is running the cold supply just dies. It is easy to get it flowing again by de-mounting the HEP pipe next to the shower pump. This airlock has happened about 4x now.

I am a bit confused about why an airlock would persist as far as I can see it the only change to the plumbing I have made is to reduce air in the hot feed to the shower....???

I realise that the cold feed to the shower should have its own tank connection (tee-s off 22mm feed to cylinder), but the system was working with this arrangement without airlocking before I did any work on it...

Any thoughts or advice appreciated....

 

[Steelmasons]

A dedicated cold feed down service from CWSC to pump should be installed.
You went to the trouble of installing an Essex flange but did nothing regarding the cold feed?

 

[grobsy]

thanks for your reply. I was thinking a dedicated cold feed might be my next step. I have now installed a dedicated cold from tank and they are still getting airlocks. First the cold to the shower shuts off and then hot gets airlocked if they dont switch off immediately...

I dont know if I made it clear in my original text but the customer didnt have airlock problem with the original set up - Only a noisy shower pump , which had to be got rid off half way through a shower by turning a hot tap.

I dont know what I have done by making the system more correct which is causing the airlocks???

cheers G.

 

[terryplumb]

have you checked the cwst is filling OK, no chance the pump is draining it quicker than it is filling ? the new outlet from cwst feeding dedicated supply to pump ,is it higher than the outlet to hwc, and what height from base of cwst ?

 

[grobsy]

cheer Terry, that will be the next thing I check. CWSTank is approx 500x500x900 with a fairly poor replenishment rate. I will run the shower and sit and watch the water level. Will let you know how this goes....

 

[terryplumb]

also consider other demands on plumbing when shower on use, I.e. other people using basins /sinks etc and of course washing machines/dishwashers etc. anything drawing off the cold main will result in the cwst filling even slower and of course same if any hot being drawn off tank drains even quicker. as your problem is not every time the shower is used but " now and then " it would point to a given set of conditions on that day.how many people live there ? mums washing dishes and putting washing machine on whilst dads in shower suffering !!!!!