What is the point of C-plan?

[Roger Mills]

Thermo-syphon hot water systems have been around for a lot longer than you or I - almost certainly before Renault built any cars!

I wouldn't use it in a domestic hot water system *today* but in 1968 when I installed my first system it was still the accepted way of doing things.

As I have said many times, no-one would install a new system based on C-Plan *but* converting a basic gravity HW/pumped CH system to C-Plan is an acceptable way of improving its control and efficiency without too much upheaval.

Yes

Yes

So, exactly how would *you* wire those in such a way that, depending on which demands are present, the boiler will run with just the pump or just the valve - or both - and when both demands are satisfied, the boiler shuts down and doesn't waste energy cycling on its own stat?

Let's see your circuit diagram!

By using the valve's auxiliary changeover switch in a particular way, C-Plan achieves all of the above.

[Lieutenant Scott]

I don't remember you referring to a diagram, but I found one:

you said cunning, I thought you meant something more complicated! I have a degree in digital microelectronics so CH systems are not rocket science :-P That looks very much like what I have in my 2 valve system, but with only 1 valve. I was imagining the valve only having a 1 way switch, and added a relay.

[Roger Mills]

>> When you said cunning, I thought you meant something more complicated! I

The clue is in the word CHANGE-OVER which I used in nearly all my posts on the subject! Cunning in the sense that, by wiring it that way, you avoid the need for any relays.

I think it's time we closed this down! So, to answer the question once and for all "What's the point of C-Plan?"

• It's NOT the answer to every maiden's prayer

• It's NOT suitable for new installations

• It has very limited application, but

• It IS an extremely useful conversion for *existing* gravity HW/pumped CH systems because it gives independent control over HW and CH and provides boiler interlock.

End of!!

[Lieutenant Scott]

>>>>> When you said cunning, I thought you meant something more complicated! I

Hardly cunning, you've just put the relay inside the valve.

I got the last word in ner ner ner ner ner?

[Lieutenant Scott]

Is it a good idea to override the cylinder stat? Why would you want the water hotter than what you set the stat to?

[Lieutenant Scott]

divides into three (it was two, but I modified it!) to go through three independent valves. One goes to the heat exchanger in the hot water tank. Another goes to the radiators in the house, the other goes to radiators in the garage (I converted it to a parrot aviary, and electric heating is expensive!).

you have to heat the water when you heat the house (or is it the other way round?). My parents boiler is set up so they have to heat the water when they heat the house. What if the house is too cold, but you aren't planning on taking a bath that day? I know the heat from the tank will eventually seep out into the house, or get used later as hot water, but it seems daft to throw heat into something you don't want right now.

It failed to meet EU regulations.

[Graham.]

hotter than what you set the stat to?

It's an old thread but I just rediscovered it so I'll respond.

The cylinder stat is in the loft so not really accessable. It's set to a lowish temperature for economical hand/dish washing, but at that temp there isn't really the volume of stored water for a good hot bath-full, hence the "boost" switch. It's served us well for 30+ years.

[Roger Mills]

water hotter than what you set the stat to?

It would, in that case, be better to have *two* cylinder stats - set at two different temperatures - with a change-over switch to define which one is to be used. That way, you'd preserve the boiler interlock feature, enabling the boiler to shut down once whichever stat was in use was satisfied.