Pump problems

[lucly]

I ieed help pls .
The system is :an electric boiler ,pump for flow,3 port valve, open dhw cylinder and a second pump which is connected to the dhw pipe, out to the consumer .The problem I have is that the second pump, (dhw /shower/tap) is running more or less all the time even though no one is using the hot water(no drips)and is very noisy !
I wonder, if I install a one- way valve (check valve ) at the outlet of the pump, will it keep the pressure on the pipe,so that the pump is only running when the tap/shower is in use.
I wonder if any of you have any ideas?
Thanks

[sonray ltd]

you need to check the pump first.
is it a pump with an expanssion vessel on like a stuart turner or salamander pump ?
it may have a sticking flow switch or vessel under pressurised.

[lucly]

the pump is a old stuart turner monsoon n1
no expanssion vessel

[yammas]

It sound it could be a fault on the flow switch, which could be jammed, or leak on system
If you go to stuartturner.co.uk and download their fault finding literature or call out a plumber to have a look