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
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