System with 2 pumps prob

[John2512_00]

Hey,

Was working in a house today where the upstairs radiators were heating on hot water,

Was a wall mounted system boiler (dnt actaully remember what one) with hw flow and return pipes on the left of it and the same for the CH on the right,

The CH had a pump just above the boiler and the HW Cylender had another pump up near it.


Now i know you can get valves that stop the hot water rising through gravity through the rads when the hw pump is on but i wanted to know what could cause this to happen suddenly? the people in teh house had lived there for 8 years and never had it so why now?

thanks for any suggestions

 

[ChrisR]

Perhaps there is such a valve fitted which now is "letting by" - dirt.

Otherwise a restriction - dirt, air - in the HW cct would increase pressure on ch circuit.