Gravity fed or Pumped?

[jpm777]

I am in the process of replacing my HW & CH programmer. The current Siemens RBW9 unit has the dip switch (5) set as gravity fed. However, I have a grundfoss pump and what I believe to be a Y-plan system with a three way valve, hot water cylinder in the airing cupboard with a cold water tank and small expansion tank in the loft. Please could someone confirm if it is fully pumped as I suspect and if so the difference in terms of operation with it having been set to gravity please? Photos below of the airing cupboard arrangement in case it helps.

 

[flameport]

It's fully pumped.

The difference is that with it set to Gravity, you can't have heating only - heating must be used with hot water all the time. Gravity is applicable to old floor standing boilers which have 4 pipes, 2 for the hot water where circulation is due to convection only, and 2 more for the radiators which are usually pumped. Such systems are inefficient and should all have been replaced long ago.

If it's been set to Gravity, it's fairly likely the wiring is incorrect, as it may have been set that way to cover up some other problem.

 

[jpm777]

It's fully pumped.

The difference is that with it set to Gravity, you can't have heating only - heating must be used with hot water all the time. Gravity is applicable to old floor standing boilers which have 4 pipes, 2 for the hot water where circulation is due to convection only, and 2 more for the radiators which are usually pumped. Such systems are inefficient and should all have been replaced long ago.

If it's been set to Gravity, it's fairly likely the wiring is incorrect, as it may have been set that way to cover up some other problem.

Thanks for the reply and explanation. Is there any way I can check if it will work fine set to pumped? The house was built in 2005 and originally had a Worcester Bosch 19/24cbi, I have recently had this changed for a heat only Viessmann 100-W.

 

[Johnmdc]

Is there a wire connected to terminal 1 at the programmer? If there is then it should work set to fully pumped.

 

[Johntheo5]

Thanks for the reply and explanation. Is there any way I can check if it will work fine set to pumped? The house was built in 2005 and originally had a Worcester Bosch 19/24cbi, I have recently had this changed for a heat only Viessmann 100-W.

You can probably check it by leaving the dipswitch at gravity, ensure the cylinder (stat) is calling for hot water then with CH only selected and roomstat calling/boiler running see if the cylinder zone vale is open, if it is, change the dipswitch to pumped and see if it now closes.

 

[ianmcd]

just set it to fully pumped and select heating only if the boiler fires then its fine

 

[jpm777]

Is there a wire connected to terminal 1 at the programmer? If there is then it should work set to fully pumped.

Thanks. Yes, there is. The only one without a wire connected is terminal 2.
Here is what it looks like to confirm as well as the wiring diagram from the RBW9 programmer.

 

[jpm777]

just set it to fully pumped and select heating only if the boiler fires then its fine

Thanks I will give it a go.

 

[jpm777]

You can probably check it by leaving the dipswitch at gravity, ensure the cylinder (stat) is calling for hot water then with CH only selected and roomstat calling/boiler running see if the cylinder zone vale is open, if it is, change the dipswitch to pumped and see if it now closes.

Thanks for the comprehensive way to test. I’ll try it first and confirm using this.

 

[jpm777]

It works! Thanks everyone for their help.