shower pump

[pilgrim]

Hi. New to this forum but old to plumbing (68 and semi retired now).
I installed shower pump about 9 months ago (with independant supplies h&c ) and correct surrey flange to cylinder. Fitted in bungalow and feeds 1 shower only. Problem now arising is when hot tap in bathroom ( not the shower room pump feeds) it brings on the pump occasionally, and according to my client it carries on for about 2 minutes and then shuts off ( or if shower is operated it then closes correctly). Any ideas? Client tells me its only on hot water side does it bring on shower pump. Both bathroom and shower are all fed from CWS storage tank. No mains cold involved. I personally have not experienced this at their premises. Every time I go it works ok but they are not clients that would say something that did not happen!
Help/suggestions please.
John

 

[Riley]

It's probably some sort of water shock I'd imagine non returns on the other appliance will help

 

[steadyon]

I'd suspect an airlock somewhere. Have had a similar issue, although run on was a matter of seconds, not minutes, cured by getting rid of airlock in the DHW circuit.

Given it's in a bungalow I'd guess you have very low pressure to the bathroom, so I suspect non-return valves would have to be of the vertical flap type or they'd offer too much resistance.

 

[Plumbstar Tom]

It's probably some sort of water shock I'd imagine non returns on the other appliance will help

I would go with this, had it before. You can often check by slowly closing off the suspect tap. It is the ceramic disc cartridge that shuts the water off almost instantaneously which cause a shock wave