there's no reason why the valves can't be after each system is there? they only stop and start the flow, so that can be after the rads and HW coil can't they - just like the pump...
impressive! i particularly like your use of colour....
on your diagram though you have valves and pump before HW tank/coil and rads (your typical s plan). is it quite feasible to have them after? in other words, does my original system make sense?!
this is definately how the old system was piped up. when HW only was called the HW valve opened, the pump started running, and the boiler fired - although the valve was knackered so this actually couldn't be tested. when CH was called the CH valve opened, the pump started running, and the boiler fired. when both CH and HW was needed both valves opened, the pump started running and the boiler fired. on all cases the system stopped when the approriate thermostat(s) were satifsfied (and there is NO pump overrun).
can you tell me how this system worked unless the valves were on the return. i have no idea. can you also label pipes 1-3 with where they are going/coming from. they run under the floorboards so i have no idea.
my theory is the valves are on the return. pipe 1 comes from the rads (pipe 1 definately heats up with the CH but the rads seem to be hotter than this pipe, suggesting a return?). pipe 2 goes back to the boiler (pumped for both HW and CH) and pipe 3 is the flow to the HW tank, to the coil and then to the HW valve (also the expansion tank). underneath the floorboard i think is a T piece which splits the water from the boiler between the HW tank and rads and can only flow if the valves on the return are open. is this feasible? any other ideas?
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