Pump overrun

[Axel]

I am soon to reconfigure my CH. Currently, my Potterton Kingfisher CF boiler has an open vent and separate feed from header tank, a pump on the flow to the cylinder via a 2 port valve, and another pump on the return from the rads. There are 2 further 2 port zone valves for upstairs and downstairs.

I am considering ditching the header and fitting expansion cylinder, safety valve, filling loop etc, due to air problems. I will also be putting CH pump on the flow side. Potterton manual recommends I connect pump to boiler directly to facilitate pump overun on fully pumped systems (at the moment pumps are activated directly by stats (relays used on 2 CH zones). But when the call for heat or HW stops (when stats are satisfied,) the only route for pump to circulate water will be via an auto bypas valve that will be fitted directly after pump, so my question is: Is there any point in having the pump overrun enabled if all it's going to do is pump water around a couple of metres of pipe in and out of boiler (as all the 2 port valves would be closed in that state)?

Secondly, would it make sense to just have one pump on flow for both CH and HW, seeing that there is a 2 port valve around every bend? ( would need to do this anyway if pump overrun used, unless I make some sort of crude relay logic circuit...)

 

[bengasman]

Just follow the manufacturer's instructions, all of them, and you will be fine.

 

[Axel]

MI's are ambiguous regarding pump wiring etc, that's why I posted this topic!

 

[kevplumb]

Is there any point in having the pump overrun enabled if all it's going to do is pump water around a couple of metres of pipe in and out of boiler

thats what its for

 

[Axel]

For last 10 years it has functioned well without pump overrun; never tripped overheat stat...only difference will be I am converting from open vent to sealed system - is this more likely to require overrun?

 

[bengasman]

MI's are ambiguous regarding pump wiring etc, that's why I posted this topic!

Could it be that the MI are correct and your expertise is ambiguous? Boilers don't come much simpler than a kingfisher. Valve on/off, pump on/off, connect to wiring centre, the end.

 

[Axel]

As there are currently 2 pumps, it would not be as straightforward as to connect both in parallel to boiler...I inherited the whole setup and am wondering how far to modify it back to MI layout,.

 

[bengasman]

For last 10 years it has functioned well without pump overrun; never tripped overheat stat...only difference will be I am converting from open vent to sealed system - is this more likely to require overrun?

Overrun, bypass, and all other provisions are to be installed exactly as required by MI, really can not make it any simpler.

 

[Axel]

RTFM is what you are trying to say!

I was simply wondering about the effectiveness of overrun in a system with 2 x 2 port valves, as there is literally only 2 metres of pipework for water to be moved around during overrun.

My second question was - why is there is a separate pump to HW cylinder, even though that circuit has its own 2 port valve? I doubt if it needs the extra circulation power of a 2nd pump, especially considering it is directly above the boiler. I would have to go to a single pump system to facilitate overrun.