I want to improve my gravity fed hot water by adding a pump

[Fastlearner]

Thanks again everyone,
It is now abundantly clear that the definitive guaranteed method is as suggested by Ironman and confirmed by IKM today.ie 2 pumps/2 x 22mm valves connected as 'S' plan.
However there is a strong temptation to approach as a 2 stage operation ie. 28mm valve/2nd pump to HW & connect to CH pump via white wire as 'C' plan.This eliminates my original problem of electrical feedback.Stage 2 being to fit the 22mm zone valve to CH if there is conflict with water flow in CH circuit.This is essentially Picasso's approach.
I am minded that because the boiler has 4 connections backflow is an unknown quantity.I am also minded of Ironman's reservation regarding throttling back of the HW pump valves.This probably will determine that a zone valve will be be required in the CH circuit.
Because this option will not involve any extra work & i have the flexibility
to change the setup from 'C' plan to 'S' plan fairly easily, it seems like a good result for me. I need to source another valve & this might as well be the 28mm version.IKM Thanks for tip on 28mm compression. If i go forward as current thinking that will apply with the 28mm valve, but i intend to use Yorkshire solder fittings for the 28/22 reduction.All in all a good result for me unless you have any strong objections.
Many thanks again
Ron

 

[IKM]

Ron,
I agree with you on the 2 stage approach which will save you some time and effort if it all works first time. I also have a Gloworm boiler with 4 connections and didn't have any problems. I chose a pump with 5m head (DAB EVO VA55/130 from BES Mail Order), set the speed to minimum and fully opened the ball valves in the coupling either side of the pump.
Good Luck.

 

[Fastlearner]

Just a final thankyou to all contributors to this discussion & a special thank you to Ironman 1 who has nursed & encouraged me throughout, in the face of adversity( just shows how fried my brain is------- had to resort to dictionery to spell throughout)
A word of caution to any outside interested parties; There have been several questions by me which have been confused, particularly 'electrical backfeed' when the respondant has been referring to 'water flow backfeed' in the CH circuit.
Ron