What sort of pump do I have on central heating return pipe

[JackK]

Hello fellow members - Really appreciate your advice here

I have an old floor standing potterton boiler which is heat only and I can see one flow and two return pipes at the boiler. Its difficult to trace the pipework through the house so thats all I know. Its also a one pipe system and barrel steel pipe so old!

Interestingly enough the pump is a green DAB pump on the return not the flow which is really strange.

I am changing the boiler for a new heat only boiler and had a question

1) Is it worth removing or replacing the existing DAB pump with a new one as it is 20 years old
2) Should I put a grundfos pump on the flow pipe as well which I think is the standard way these days? If so should i remove the pump on the return pipe?
3) Is the current green pump set at max circulation speed as one radiator (which I recently added) does not get any heat to it as it is on end of pipe run

Thanks all

 

[cross thread]

If upgrading to a new boiler the system will need some updating, not just a pump replacement.

 

[fixitflav]

Should I put a grundfos pump on the flow pipe as well which I think is the standard way these days?

If you put a pump on the boiler flow you will need to re-think the open vent and cold feed.
As well? I suppose you could leave the old pump in (switched off) and let the water flow through it, but that would be a bit of a bodge. Better to take it out and put in a length of pipe.

 

[JackK]

Thank you - Just so that I am clear - I am replacing the boiler - If I want to replace the pump at the same time should I leave it on the return pipe like it is at the moment?

Can I use a grundfos pump or do i need to stick with a green dab pump (which seems to be for water)

I am trying to swap a boiler which no longer works and have a gas engineer to do the boiler but i will do the pump!

 

[polesapart]

On a "one pipe system and barrel steel pipe so old" I would not change the pump position without a good understanding of the hydraulics of the system and in particular the feed and vent arrangements.

If upgrading to a new boiler the system will need some updating, not just a pump replacement.

^^
+1

 

[dal5band]

I think the reason for checking the feed and expansion arrangement is that if you put the pump in the flow, it may pump water up into the expansion tank continuously.

 

[fixitflav]

Thank you - Just so that I am clear - I am replacing the boiler - If I want to replace the pump at the same time should I leave it on the return pipe like it is at the moment?

Can I use a grundfos pump or do i need to stick with a green dab pump (which seems to be for water)

I am trying to swap a boiler which no longer works and have a gas engineer to do the boiler but i will do the pump!

If you put the pump on the flow it should be boiler – open vent – cold feed – pump. Maximum 150mm between open vent and cold feed, to minimise risk of flow out of the vent pipe, and cold feed up and under into the pipe to reduce risk of convection warming the F/E tank which encourages mould growth. The other bits don’t need to be near the boiler.

You could use a Grundfos, but I doubt you need a £700 model. You might consider stripping down the pump, giving it a good clean, and repositioning it.

Also your pump appears to be pumping downwards, which is non-preferred.

I had a system originally like yours, I moved the open vent, cold feed and pump to the airing cupboard and added a diverter valve.

Without seeing the house can’t say how practical it would be to change things

 

[JackK]

Hi fixitflav - many thanks indeed –

1. Can you just clarify what you mean by "If you put the pump on the flow it should be boiler – open vent – cold feed – pump. Maximum 150mm between open vent and cold feed, to minimise risk of flow out of the vent pipe, and cold feed up and under into the pipe to reduce risk of convection warming the F/E tank which encourages mould growth. The other bits don’t need to be near the boiler."?

I have a boiler at ground level, the pump at the ground level on the return pipe, a cylinder at first floor and a F&E tank in the unused loft. Cold feed to f&E tank is a pipe about 200mm from rising mains into the F&E tank. There is a two port valve at the first floor airing cupboard

1. I want to change the pump – It is downwards on the return pipe – Can I remove it and put it on the flow pipe or should I keep it the same direction and position?

What did you do in your house and why did you used a diverter valve

 

[denso13]

Can you just clarify what you mean by "If you put the pump on the flow it should be boiler – open vent – cold feed – pump.

 

[fixitflav]

There is a two port valve at the first floor airing cupboard

In that case yours is probably gravity HW i.e. convection flow between the boiler and the coil in the HW cylinder (the primary circuit). Does your boiler have 2 flow connections, one to the pump, the other to the HW cylinder?

What did you do in your house and why did you used a diverter valve

Mine was originally gravity HW. Nowadays the accepted way is fully-pumped, so I converted. This needs either two 2-port valves (S-plan) or a 3-port valve (W or Y-plan). I went for W-plan as it's simpler and I don't think Y-plan (with mid-position valve) gives significant advantage. In fact, if weather compensation is retrofitted to Y-plan it has to be reconfigured to eliminate the mid-position.
My airing cupboard is directly below the F/E tank in the loft, so bringing the vent and feed pipes there was straightforward. Don't know whether yours is similar, if you want to do something like that.

I want to change the pump – It is downwards on the return pipe – Can I remove it and put it on the flow pipe or should I keep it the same direction and position?

The new boiler will have 1 flow and 1 return connection. I suppose you could keep the pump near the boiler and pipe the flow to it (preferably pumping upwards), which means bringing vent and cold feed to that area. Or you could have the pump on the return, also bringing vent and cold feed to that area.
It mostly depends on the layout of your house.
Also don't forget that after re-piping, the rad returns must all be commoned before joining the cylinder return, or there'll be unwanted rad warming when only HW is called.