Shower pump turns in when cold water ran downstairs?

[CaptainJack88]

We've had our shower pump installed for almost a year, and before that the previous owners had 2 separate pumps for the ensuite and main bathroom.

We haven't changed the pipe layout and the only thing we did was install a flange for the hot water in the tank.

Yesterday when both showers were in use for quite a while, the pump just stopped. It wouldn't turn on for hot water but cold water was fine. I gave it a few hours and the hot water was being pumped again.

I then started noticing than in random occasions the shower pump would turn on and the off when the water was ran downstairs.

What doesn't make any sense is that the cold water feed for these taps comes from the mains and it doesn't go anywhere near the pump for the showers, they're a separate dedicated set of pipes for each shower on the other side of the tank, with the cold water coming from the header tank

Has anyone got any suggestions? Could an air blockage cause this?

 

[CaptainJack88]

Updated with a diagram. Essentially, tap downstairs is turned on and when turned off, the pump blasts for a second

 

[Newboy]

1) When the pump stopped after prolonged use it may have:

a) overheated and thermal overload protection kicked in and reset after the pump cooled sufficiently.
b) You may have partially drained the cylinder - two showers going at the same time may have been pulling out water faster than the tank could refill

2) When the downstairs tap is closed (suddenly) it may be sending a pressure wave back up the pipework sufficiently strong enough to trigger the flow switch in the pump or possible cross-flow from the mains cold back along the hot pipe causing the same effect.

 

[CaptainJack88]

1) When the pump stopped after prolonged use it may have:

a) overheated and thermal overload protection kicked in and reset after the pump cooled sufficiently.
b) You may have partially drained the cylinder - two showers going at the same time may have been pulling out water faster than the tank could refill

2) When the downstairs tap is closed (suddenly) it may be sending a pressure wave back up the pipework sufficiently strong enough to trigger the flow switch in the pump or possible cross-flow from the mains cold back along the hot pipe causing the same effect.

Well the second part makes sense regarding the pump giving a blast, but why would it only just start?

EDIT: Can confirm point 2 is correct. Its only on the hot water when stopped suddenly.

I dont understand why this would happen though as the flange would stop the water from going to the pump, so it has to be causing a fairly big pressure change in the tank?

 

[phod]

Possibly have pulled some air into the hot side of the pump/pipework.
shockwaves from tap turning off compress the air, making the water move and triggering the pump flow sensors.
might also explain why hot didnt run for a while too.
Turn the pump off at the mains and run hot through each shower outlet, with showerhead removed, in the hope you might purge some air.

 

[CaptainJack88]

Possibly have pulled some air into the hot side of the pump/pipework.
shockwaves from tap turning off compress the air, making the water move and triggering the pump flow sensors.
might also explain why hot didnt run for a while too.
Turn the pump off at the mains and run hot through each shower outlet, with showerhead removed, in the hope you might purge some air.

OK, i'll give it a go. I thought air would have come into play somewhere, but thought that was the whole point of the flange.

I don't really know how the air would have gotten in their though. The only way for air to get in there would have been via the header tank, but I can't imagine that was drained to the point it was empty, allowing air to get into the system.

 

[CaptainJack88]

Must have been a lot of air in the system, one of the shower pretty much just exploded on me!

Seems to be sorted now though!

 

[Newboy]

If you pull more water out of the cylinder faster the cold feed can replenish then the air will be drawn down the vent pipe

 

[Steelmasons]

I doubt whether any check valves were fitted.....

 

[CaptainJack88]

If you pull more water out of the cylinder faster the cold feed can replenish then the air will be drawn down the vent pipe

Ah, I never thought about that.

Where would the check valve be fitted in the system?

 

[vinn]

If I understand what you are saying OP, then you only have the one storage tank (what size?) for the shower and for the domestic side eg. what happens if the w/m or d/w comes on as you are taking a shower - my take is to install a dedicated shower feed tank.

 

[CaptainJack88]

If I understand what you are saying OP, then you only have the one storage tank (what size?) for the shower and for the domestic side eg. what happens if the w/m or d/w comes on as you are taking a shower - my take is to install a dedicated shower feed tank.

The only thing that is actually fed from the header tank is the bath, shower pump and both upstairs toilets Fortunately, if you're taking a shower, you probably won't be flushing the toilet! Everything else is from the mains supply. w/m, d/w etc are all cold feeds

I'm not sure what size the tank is to be quite honest with you. It's the original from when the house was built (1995) for a 4 bed - (2 upstairs bathrooms, 1 downstairs toilet) If I were to guess, I'd say 175 - 200 Litres?

 

[vinn]

Thanks for the further information but I've just glanced up at the OP and the diagram, and maybe my best advice now is for you to get a plumber in or one of these guys who specialises in showers.