Shower pump surging

[fingers88]

I have a pump feeding separate hot & cold to a shower thermostatic valve. It has started to "surge" meaning that it goes on and off quickly so pumps water in surges about once a second. It has done this a little in the past and has easily been remedied by turning up the flow in the shower. However, I cannot cure this now by increasing pressure, more hot than cold and vice versa. Also removing he filter from the shower to reduce resistance doesnt work. The only way it runs properly is when i remove the shower hose altogether and the water flows form the valve attachment. The shower attachments are clean with no obstructions so I think it is the pump that is at fault.
Admittedly it is quite old so may well be past its best.
Any thoughts?
I haven't mentioned the make or model as I don't think that is relevant but it looks like a standard pump.
Thanks

 

[j1cta]

Fingers,

These pumps are quite sensitive and usually "surge" because they experience reverberations in the flow of the water, sometimes called "hammer". This is usually predominant when you turn the water off and the reverberations continue back and forward down the pipe.

I've never heard of it while the outlet is turned on, but I would suggest the usual remedy.

The usual way to solve this is to install a check valve on the hot outlet to prevent any vibrations returning to the pump.

Drop one in and see how that goes!