Plumbing (central heating) quiz. A beer to the person who helps me figure this out successfully.

[kp7722]

In my previous post I described how I've messed with my current CH & HW system to make it fully pumped (S plan). I think I've messed up a perfectly good system but it is totally undo-able. What I need to know is from the following information would the old system have worked successfully so I had HW only when I needed it, CH only when I needed it, and or both. And would it have been fully pumped?

the diagram:

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 (the valve was set to manual open). 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?

Cheers, Paul.

[Roger Mills]

What you've got (or had?) is a fairly conventional S-Plan fully pumped system - except that it seems to be arse about face!

Let's assume for a moment that we turn the pump round, so that the flow is upwards. Pipe 2 is then the combined HW + CH flow pipe from the boiler. After going through the pump, the water splits into 2 circuits. The HW circuit goes through the HW valve to the coil in the cylinder, out again and back down pipe 3 to the boiler. The CH circuit goes through the CH valve and then along pipe 1 to the radiators - and the radiator returns presumably combine somewhere and then connect into pipe 3 to go back to the boiler.

With the flow through the pump going downwards, everthing works exactly the same - except that circulation is in the opposite direction, with flows and returns being interchanged. That may have been done deliberately, to prevent the F&E tank from pumping over. Conventionally (with the pump going in the normal direction), the connections to the F&E tank should be in the main flow pipe (2) just before the pump.

I haven't a clue what the 15mm pipe is which appears to by-pass the pump!

The pipe labelled 'domestic HW feed?' is the cold feed into the DHW tank from the large header tank in the attic. When you open a hot tap, cold water flows into the bottom of the cylinder expelling hot water out of the top connection (labelled 'domestic HW out?') and on to the taps.

What you had - albeit somewhat unconventional - should have worked. Why did you change it?

[kp7722]

sorry Roger, I've also just noticed that I keep replying to you alone and not to the group. many apologies....

[Roger Mills]

Try to make sure that you copy them to the group, for all to see - some have been already. [I hadn't actually seen the private replies 'cos - like it says in my signature - I don't monitor the googlemail address very often!]