stuart turner pump problem

[eagleeye]

Hi all hopefully someone can help me here before I ho insane. About 6 months ago I replaced a cheap watermill twin pump for a stuart turner monsoon as the existing on kept turning on every so often during the day. I thought it was the flow switches. Customer is really happy with the pump as its much more powerful. Problem is its still switching itself on as before. I spoke to pump assist at stuart turner and they told me to isolate supplies to pump to see if it stops. Which it did. So we know pumps ok. I then isolated hot and cold separately to see what supply was causing it to switch on. Found it was the cold side. Fitted a single check valve on the cold outlet as told by pump assist. This cured it for 2 days. Now its back worse than ever. I have checked all outlets and nothing is letting by. Pump supplies whole house and shower in bathroom upstairs. Pipes for this run up from pump into loft and across 2 mtrs and down wall to shower valve.
Can anyone help me here as its doing my head in now. Fitted loads of stuart turner pumps and never had trouble like this

 

[stevetheplumber]

if the check valve cured it for a while i would try another one there not the most reliable of fittings and i would add another on the hot while i was there . Other than that check for any leaks as you say the st pumps are usually pretty good
House or flats ?

 

[Gray0689]

Sounds like you could have a leak

 

[IDCHAPPY]

Sounds like you could have a leak

This^.
If it's fine when isolated from the house, then starts running for no reason when you turn on the house valve then there's a leak.
If it does both hot and cold then check the toilet/cistern, i had one in a hotel doing a similar thing and it was the cistern passing water into the toilet bowl, not a visible leak but enough to kick in the pump every few mins