Hi ime not a plumber so go easy new here .Due to lack of finances ime fitting a grundfoss central heating pump myself as the old one died on me,stupidly i forgot to take note of the arrows on the original pump re the correct direction of flow.The pipework i can see is some way from the back boiler and is horizontal and i am unable to see which pipe is the flow and which is the return.So my question is how can i tell which way round to fit the pump ?should the arrow go from right to left if the right pipe to the pump heats up first or is it the reverse@help as ime worried about knackering the system. sorry if this is maybe a stupid question ,.