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If I am looking at your boilers M.Is then 4.3 - "a variable duty pump should be set to give a temp diff of no greater than 20deg C"
"Important F&R pipe sizes - up to 18kw = 22mm, >18kw =28mm"
The flow rate required to provide 18kw @ 20 degC would main that your pump would loose approx 1M head just pushing that amount of water through the heat exchanger if you needed it full 30kw you would loose over 2.5Metres.
Your existing pump is a 5M head but that is the max it can push with no or little flow. Moving approx 0.215L/S it would only develop a pressure of approx 3.7M head, less the boiler 1M, would leave approx 2.4 M for the rest of the system. Not likely to be enough to overcome the resistance you have put in by re-piping in 10mm.
"Important F&R pipe sizes - up to 18kw = 22mm, >18kw =28mm"
The flow rate required to provide 18kw @ 20 degC would main that your pump would loose approx 1M head just pushing that amount of water through the heat exchanger if you needed it full 30kw you would loose over 2.5Metres.
Your existing pump is a 5M head but that is the max it can push with no or little flow. Moving approx 0.215L/S it would only develop a pressure of approx 3.7M head, less the boiler 1M, would leave approx 2.4 M for the rest of the system. Not likely to be enough to overcome the resistance you have put in by re-piping in 10mm.