Gravity DHW --> pumped

[Pgreen]

I have a gravity DHW/pumped CH system. On the DHW side I have a cylinder stat on the DHW storage cylinder which operates a motorised valve to control flow from the boiler to the storage cylinder. To speed up DHW heating times, could I simply replace the motorised valve with a small water pump ? My thinking is that when DHW needs to be made the pump would actuate and shut off when DHW requirement is satisfied. Flow through the pump when DHW is not required should be minilmal ( ?). As a retrofit, I think this would be simpler than fitting a motorised "T" valve and using the existing pump. Also, if this idea could work, any recommendations on what pump could do the job ? My guess is it doesn't have to be as big as a standard CH pump since the gravity DHW only needs to be helped along.

many thanks in advance.

 

[gas4you]

Putting a pump in the gravity circuit will impede the gravity circulation, do a standard 15/50 pump is what you would need.

Your problem might be the pipe work arrangements, cold feed and open vent, as the new pump could cause pump over and/or suck in air if fitted in the wrong place.

Search FAQs on here for pipe work diagrams, ChrisR has posted many good diagrams in the past.

 

[Breesey]

...And there would be no way of controlling CH only if there was no way of closing primary flow to DHW. It is required that this is possible ie seperate controlled heating and HW zones

 

[bengasman]

Yes it would be simpler, but unfortunately not much chance of working properly.
Best way to make it safe, reliable, and economical is convert the whole thing to y-plan.
No way of doing it cheaper AND correct