Intermittent Negative shower pump

[fergal]

I have fitted a Salamander negative head shower pump to my system for a new bathroom in an extension. I measured the cold water mains pressure at 3 bar but needed equal pressure for the hot. Salamander technical said that I could use a single 3 bar pump for the hot fed by the gravity system. The shower head is roughly equal to the bottom of the water tank hence the negative head pump.

The pump is located in the airing cupboard and fed using the salamander valve. All pipework is 22mm. The problem I have is that when the shower is turned on (thermostatic shower valve which says minimum pressure should be 3 bar and maximum 5 bar) the pump has been turning off for a split second every 20 seconds or so and starting again. This only happens when the shower is on. If I turn a hot tap at the same time as the shower then the pump runs continually. It seems to me that the pump is building up too much pressure feeding the shower (which has half inch inlets). The real strange thing is that this didn't happen at all for the first few days that the pump was installed.

I there a way of stopping this from happening?

Obviously I'm going to go back to Salamander technical but I'd appreciate any other thoughts or opinions.

 

[reggie09]

had a similar problem with one i installed, customer called me back saying pump cuts out after a few seconds then kicks back in cycling on/off when ever shower is in use, after investigation i found that the customer had left the shower head inbetween settings so the restriction was reducing the flow down to the point where the switch could not sense the flow, try it without the shower head on see if the pump stays on, if so thats the problem, if not disconnect the flexi pipes on the pump(showerside) and discharge into a suitable container see if the pump stays on, if this doesnt make a difference then u know its not the flow through the pump.

 

[fergal]

Thanks Reggie but after giving it some thought overnight I think it is more likely that the mains cold water pressure has increased and is backing into the shower pump via the thermostatic valve. I took pressure readings on two occasions for the mains and both times pressure was around 3.1 bar so the pump was able to deal with this and work normally. I now remember that there was an awful lot of digging roads up in the town and it would appear that major water works were in progress. I think that if I took a pressure reading now their mains pressure will have increased so it's too much for the pump. I'll see over the weekend if this is a permanent increase and if it is I can easily install a water pressure reducing valve to the bathroom cold feed.

Thanks again for your help though

 

[Jamie Plumbteq]

Hi Fergal

A negative head pump only needs to maintain it's set pressure once it does the pump shuts off and when the pressure drops again the pump kicks in, as there's a higher demand when you switch your tap on the pump will run constant to replenish the pressure but may not need to replenish the pressure as quickly when only the shower is running hence it cuts off for a few seconds.

if there's no problem on the shower outlets your pump is doing it's job, a positive head pump works different it should be on from when the shower is on until it is closed off.

hope this helps, cheers Jamie