Pump over-run - location for by-pass valve

[firebladerrw]

Hi,

I'm about to get new Potterton condensing boiler fitted which has a pump over-run feature, basically to take any excess heat away from the boiler after its been switched off from the programmer. Therefore a by-pass valve will need to be fitted after the pump (to the return line) to ensure flow.

The pump is remote from the boiler (airing cupboard), and immediately after the pump (see picture).

Obviously when the system isn't calling for heat from either the DHW or heating side, both 2-way valves will be closed.

So the question is, where should the b-pass go? on the DHW circuit before the solenoid valve, or the heating side, or does it matter? I should mention that the radiators on the heating side all have TRV's except one.

Thanks in advance

 

[petit_pablo]

The bypass should be after the pump, before the valves and go to the primary return. Idealy an auto bypass should be fitted so the flow rate can be set for your boiler

 

[Gasguru]

While you're at it replace both zone valves.

The top one is ancient and on borrowed time, the lower one's a carp Sunvic and will leak around the spindle or seize. Go for a couple of Honeywells.

Also replace those rubbish pump valves with proper gate valve types. Again they will eventually leak around the spindle.

Looks like the magnacarps on the flow...might last longer on the cooler return (and help the boiler).

Honeywell DU145 for the bypass.

 

[firebladerrw]

Thanks, I should have said that the primary return is either under the floor or wall, so can't get at it without major wall surgery. That's why the magnaclean is located where it is too !

Comments noted on solenoid valves, they are bout 15 years old-but still working ! Due a change probably !

 

[petit_pablo]

Looks like you'll be lifting some floorboards then!

 

[corgiman]

might be better to change the system to a y plan

no bypass nescessary then

 

[ctp]

might be better to change the system to a y plan

no bypass nescessary then

this advice is your best option and the crap in the system has allready gone through all majour organs b4 it gets cleaned move it to the rtn pipe,

 

[firebladerrw]

might be better to change the system to a y plan

no bypass nescessary then

Thanks

Could you elaborate please? do you mean use a 3 way valve instead of 2 x 2 way valves? Surely if both were closed I'd still need a bypass for the pump over-run?

I cant fit the Manaclean anywhere else, as the return pipe is under the floor and there is no room at the boiler. When the new boiler goes in, I'll have a look at the pipes to see if can fit it somewhere.

 

[petit_pablo]

Could you elaborate please? do you mean use a 3 way valve instead of 2 x 2 way valves? Surely if both were closed I'd still need a bypass for the pump over-run?

A 3 way valve / Mid-position valve will always have 2 ports open at all times so the overrun will be fine.

 

[firebladerrw]

Could you elaborate please? do you mean use a 3 way valve instead of 2 x 2 way valves? Surely if both were closed I'd still need a bypass for the pump over-run?

A 3 way valve / Mid-position valve will always have 2 ports open at all times so the overrun will be fine.

Ok thanks - I kinda thought that if both DHW or heating weren't calling for heat, then both of the 'out' ports would be closed....

What about wiring? Currently there are 2 wires to each 2 way valve, I take it you can use the same connections ?

 

[ctp]

Could you elaborate please? do you mean use a 3 way valve instead of 2 x 2 way valves? Surely if both were closed I'd still need a bypass for the pump over-run?

A 3 way valve / Mid-position valve will always have 2 ports open at all times so the overrun will be fine.

Ok thanks - I kinda thought that if both DHW or heating weren't calling for heat, then both of the 'out' ports would be closed....

What about wiring? Currently there are 2 wires to each 2 way valve, I take it you can use the same connections ?

no it turns off the power on satisfid and pump overrun in boiler continues on a short timer and on a 3 port there is always 1 side open

 

[firebladerrw]

Ok sounds like a plan - I take it the wiring wont need major surgery?

ie re-wiring 2 x 2port to 3 port valve

 

[D_Hailsham]

Ok sounds like a plan - I take it the wiring wont need major surgery?

ie re-wiring 2 x 2port to 3 port valve

Here are the wiring diagrams for the two 2-port (S PLan) and one 3-port (Y Plan) systems. There are many differences but the most important, if you are contemplating changing from S Plan to Y Plan, are that the Y Plan needs a wire from the Programmer HW Off terminal and from the cylinder thermostat Sat/Off terminal. This will mean running a new cable from the programmer, which may not be possible.

View media item 72 View media item 31288
It may be cheaper, and easier to install an automatic bypass valve.

 

[matt1e]

Ok sounds like a plan - I take it the wiring wont need major surgery?

ie re-wiring 2 x 2port to 3 port valve

no the wiring is different you need an extra connection from the hw off terminal to the valve and also to the satisfied connection on the clyinder stat, also your existing 2ports will be wired to fire the boiler using their internal microswitches and as a domestic 3port doesn't have any then there will be wiring changes there too
how difficult it will be to convert depends on what you have now in the way of cable cores and how its wired
out of interest what make/ model of boiler are you planning on having fitted
Matt

edit beaten to the post by Mr hailsham again lol

 

[firebladerrw]

Ok sounds like a plan - I take it the wiring wont need major surgery?

ie re-wiring 2 x 2port to 3 port valve

no the wiring is different you need an extra connection from the hw off terminal to the valve and also to the satisfied connection on the clyinder stat, also your existing 2ports will be wired to fire the boiler using their internal microswitches and as a domestic 3port doesn't have any then there will be wiring changes there too
how difficult it will be to convert depends on what you have now in the way of cable cores and how its wired
out of interest what make/ model of boiler are you planning on having fitted
Matt

edit beaten to the post by Mr hailsham again lol

Thanks to both of you - Having done a bit of trawling, I'd come to the conclusion that DH has suggested - its simpler to fit an automatic by-pass valve. That of course takes me back to the original problem, I cant get at the common return pipe at all !

Question; is it feasible to fit an automatic by-pass to the DHW side ? ie bypassing the DHW solenoid valve? That would ensure flow for boiler over-run - Just a thought.

I'm getting a Potterton free standing condensing boiler fitted.

Forgive the amateur picture, but this is a suggestion to solve the problem?