We have a fully pumped Oil fired CH. (S Plan I think, 2 separate motorised valves
one for heating, one for hot water.
I am told the pump is in the return.
Some years ago, we had some alterations (mostly addition of a shower), and the plumber said the system was pumping over (hadn't seen this before), and he extended the pipe that goes up in the air (higher) and drops down into the F&E tank.
Since then I think all has been well.
Fast forward a few years. A boy (didn't look old enough to shave), came and did some modifications last week. Added some radiators, replaced another, firred thermostatic valves on all the radiators he'd installed, replaced the pump.
Announced the system was pumping over, and that if I made sure I always turned on the hot water at the same time the heating was on, we wouldn't have any problem (my immediate thought was - what happens when the HW stat says "no more heat thanks").
Generally, he was rigt, but on one occasion it has pumped over even though both Heating and HW were on (perhaps as the syslinder stat was no longer calling for heat).
I noticed after he had left that he had the 3 position Grunfoss pump set to it's highest head/pressure/speed and I wound it down to "1" , which according to the stuff on the pump, is lover / slower than "1" on the old pump. But this made no difference.
What might have caused it to start pumping over?
What is the cheapest way to fix it (I really don't want to have him back, his plumbing of the Radiators was awful! (but I could get the builder who supplied him to supply another plumber who MAY be better)).
Could the top of the inverted U in the loft be taken even higher (there is plenty of height up to the ridge)?
Could the system be converted to a sealed system (what MIGHT need to be replaced? - Boiler (one of the original Wallstars)? Cylinder? Anything else?
I suppose I could fit a Calor Combi (but there lies MUCH capital expense and disruption).
Any other suggestions?