CH programmer terminology

[diy_dude]

I am looking for a new CH programmer to replace the existing one. There are a couple of things I dont quite understand.

1) whats the difference between a common timebase and an independent timebase? (Danfoss CP715 vs FP715)

2) Does the gravity / pumped selector simply mean can the heating run without the hot water or not?

Background:
I want to replace my mechanical single channel timeswitch. My system has one pump and one inline valve. The pump is controller by the boiler and runs for both central heating and hot water only modes. The valve operates when the room thermostat tells it to. We use this to disable the heating during the summer.

 

[plumber (new blood)]

call a pro, that way you won`t set your house on fire

 

[diy_dude]

I understand the electrical side of things, just wanted to check I understand the plumbing terminology correctly...

 

[plumber (new blood)]

hard to explian,easy to do. all comes down to how the the system is fed and operates.

 

[Softus]

1) whats the difference between a common timebase and an independent timebase? (Danfoss CP715 vs FP715)

If the programmer uses a common time base then the programmed on/off times affect both channels identically.

With an independant timebase programmer, you can set on/off times for one channel that have no effect whatsoever on the other channel.

2) Does the gravity / pumped selector simply mean can the heating run without the hot water or not?

It depends. The gravity setting is for systems that still have a gravity DWH circuit, so the programmer can turn off the pump when there is no CH demand. The thing that determines whether or not the DWH heats, or not, is whether there is a motorised valve to control the flow to the cylinder. If there isn't (as in my own archaic system) then the water will heat whenever the boiler is fired. Depending on the pipework the CH might steal heat from the DHW circuit, so there is no hard and fast answer to your second question.

I think this is what plumber actually meant to convey with his/her singularly unhelpful comments.

 

[diy_dude]

Softus: Thanks for the more informative reply.....