Should I install a 2nd pump?

[jonno]

The existing system in our new (1950s) home is very many years old comprising a 120K Bthu BF boiler by Thorn EMI and a HW cylinder adjacent to the boiler in the back of the garage - all some distance from all the rads and the bathrooms!! It has (of course) a pumped central heating system to get to and all around the bungalow but the HW system is gravity fed (ugh! ugh!) and the cylinder is right next to the boiler (ie with hardly any operating head!). Consequently I get very slow HW recovery and probably very poor HW volumes. Making matters worse, I lose heat despite improvements to the HW secondary return system to get more prompt delivery of HW to all the taps. (if only I had the space - and 'her' permission - to move all the stuff from the garage into the bunga!)

(For additional info, the boiler returns are combined to the connection below the gravity HW feed and the top up feed arrives in the gravity return before the CH return is tee'd in. The boiler expansion pipe comes off the gravity feed to the cylinder - no surprise!

I need to pump the primary circ through the cylinder. I have a spare pump but would have to buy any MVs. Should I:

A) add two MVs after the existing pump (or perhaps a mid position MV with HW priority, as at our previous home) ; or
B) (as one plumber has advised) add a second pump placed on the HW primary as this pump would have little to do (being so close to the cylinder) whereas the CH pump is set wound up to get around the lengthy CH system. I quite like this option but how should it be plumbed and wired?

I would appreciate some guidance from all the experts out there. Thanks John

 

[aggis]

Wouldn't put a pump on the HW circuit with exp pipe on flow, it'll pump over or suck air into system making more sludge to block up the system. If you went to a fully pumped system I'd certainly flush the system, maybe even powerflush it. This all could add up to a costly job .
Prob' better getting a new high effiency boiler & upgrade, especially that you've got a 120,000 btu boiler.
Would save in running costs,esp price of gas is going up.
Also getting parts for your old boiler might be difficult to get hold of, so you could end up paying for the alterations & the boiler breaks down at the wrong time.
Just worth thinking about the overall picture.

 

[Blackcatgas]

Leave it alone, or put in a new system.

 

[jonno]

Thanks for the replies received so far. Although none specifically critique the merits of a 2nd pump for the very short loop through he cylinder.

For further clarification I add that:

1) the 28mm pipe gravity flow from the boiler goes straight up to expansion (then in 22mm) but has a 28mm tee off to the cylinder. The 28mm to the cylinder is bearly 600mm long in total. Any pump would be between the 28mm tee and the cylinder inlet so I would not expect to get a problem at the expansion tank and I would also not expect to add to any sludging/flow problems. That said (and £s permitting) I agree it may be a good idea to give the entire system a good clean (powerflush and new inhibitor) but as yet the CH works fine (ie no noises or lack of performance anywhere - just the pesky HW recovery). In due course I can envisage swapping out the cylinder.

2) The boiler works very well (its old school!) and the previous owner left evidence of regular maintenance. I'm not convinced that the lightweight HE condensing boilers save any money especially in the south of England. I'd like to keep the old school boiler going as long as possible as I can see it easily outlasting any HE boiler I could install today.

3) I reckon I will end up simply reconfiguring the pipework so that the existing pump will serve 3 zones - 2 in the bunga for CH and towel rails and one for HW) - with an MV for each (ie Sundial S Plus).

4) I still hope someone will come back and critique the merits of a separate pump for the HW on the basis that the CH (very very long) and HW (very very short) circuits are so very very different.
Regards Jonno

 

[aggis]

It's not the length or size, it's the pump position & neutral point.
An HE will save you money whether in the south or north. Due to size, material of the heat exch.
Also if the system is balanced properly & the return temp is below dew point, it will save you money.
Just pick the boiler manufacture wisely.

 

[Blackcatgas]

If you really must tinker with it then convert it to a y or s plan and new controls, dont use 2 pumps, use a gate valve on the cylinder return to balance out the system.
Your Thorn EMI Housewarmer contains aspestos so dont lick it.

 

[tamz]

If you fit the pump where you are suggesting it will draw air.
Change it to an S plan. There are a few ways to do this with minimal alteration.