Adding an extra pump to heating system

[Carnegie]

I have a relatively new central heating system which has 25 radiators including 4 towel rails. The Valliant boiler, sized to provide the appropriate BTU, has an inbuilt pump but circulation to some of the downstairs radiators appears restricted and maybe the pump is having difficulty getting the full circulation. I also have a Santon unvented cylinder for hot water.

Is it possible to fit an extra pump to the heating pipework to give the system a boost.

The heating pipework from the boiler travels a long way and up and down, to get to and return from all the rads

 

[dontknowitall]

Not sure if it's possible but I'd have thought that changing the pump for a more powerful one would be the way to go.

 

[m4rkeb]

sounds like you need to balance the system and range rate the boiler to stop it ramping up. shouldnt need another pump

 

[diamondgas]

:iagree: ballancing correctly the hot water circuit and heating system should overcome the problem, if the pipe size supplying all the rads is correct!

 

[stevetheplumber]

correct way would be a low loss header and larger pump or possibly two running from that but if pipework is under sized you may have to rerun some of it
25 rads is going to be well over 100 000 btus of load so pipework needs to be 35mm minimum at the start

 

[SimonG]

I would have gone into multiple zones with valve and pump for each (2 htg and 1 hot water). Wouldn't have thought about the header though, might have to look at them for bigger installs.

 

[stevetheplumber]

I would have gone into multiple zones with valve and pump for each (2 htg and 1 hot water). Wouldn't have thought about the header though, might have to look at them for bigger installs.

i was thinking of how to add a pump i doubt if theres a upgrade for what sounds like a system boiler
but doubt if id have used a system boiler for that many rads, preasure vessel is probaly under sized as well
its obviously a large house with 4 bathrooms and 21 rads

 

[diamondgas]

Good shout steve, regards low loss header. :clap:

 

[vectra65]

had this before on a job combi system just added extra expansion vassel to system did job ok

 

[diamondgas]

Vaillant do a 46kw system boiler with low loss I believe steve ... not that I've ever fitted one mind! oooooh! me back!!! Thinking about it brought on a twinge!! :rofl:

 

[stevetheplumber]

had this before on a job combi system just added extra expansion vassel to system did job ok

id lay odds if you went and saw this install its all run in 22m anything over 50000btu needs 28 and over a hundred 35mm

 

[stevetheplumber]

I would have gone into multiple zones with valve and pump for each (2 htg and 1 hot water). Wouldn't have thought about the header though, might have to look at them for bigger installs.

how would you do that with a system boiler without some sort of header as boiler pump would still be pumping you need the header volume to disipate heat on the overrun in the good old days you could have a towel rail circuit open but not good practivce now to save energy

 

[SimonG]

how would you do that with a system boiler without some sort of header as boiler pump would still be pumping you need the header volume to disipate heat on the overrun in the good old days you could have a towel rail circuit open but not good practivce now to save energy

Would have used heat only boiler and seperate expansion vessel, as you said previously, the integral vessel will be grossly undersized. Plus I'm sad because I'm looking at it from an oil perspective rather than gas. Have to go and look at a big install tomorrow afternoon, might be big enough for a header.

 

[Blackcatgas]

Vaillant do a 46kw system boiler with low loss I believe steve ... not that I've ever fitted one mind! oooooh! me back!!! Thinking about it brought on a twinge!! :rofl:

It looks identical to an 837/637 5" flue. its about twice the price though.

 

[Carnegie]

Thanks for that - will get new plumber to investigate

 

[Carnegie]

You are spot on Steve - the pipework has been done in 22mm reducing to 15mm when rads are connected! Does this mean a complete re-pipe?

 

[sheff paul]

id lay odds if you went and saw this install its all run in 22m anything over 50000btu needs 28 and over a hundred 35mm[/QUOTE



Seen this a lot on bigger jobs,lot of plumbers dont bother increasing the pipe straight above the boiler if the boiler has 22mm connections ,they pipe on with 22mm,say for example ,Logic heat only 35kw comes with 22mm connections,you gotta increase it to at least 28mm,at the boiler.Thanks steve for the figures good rule of thumb,(old gits like us still use btu's).

 

[Carnegie]

Hi Steve-had experienced plumber round & he says primary flow & return pipes should be 35mm from boiler to valves - exactly same as you! - he said it would be ok to keep 22mm pipes for heating flow & return (after valve) & 15mm pipes teed off to rads. Any view & thanks for your help & obvious experience

 

[Henchman76]

I love this forum is the greatest thing since sliced bread.

 

[Henchman76]

Forgive me for being somewhat ignorant but what is a header ? Do you simply mean a header of water ? Please explain, many thanks chaps

 

[dontknowitall]

Forgive me for being somewhat ignorant but what is a header ? Do you simply mean a header of water ? Please explain, many thanks chaps

You know in football when they take a corner and the ball bounces off someone's head. That's a header. And a header of water is when a prankster puts water in the football.

It's a "tank" of water above the point of use. The weight of water and the height of the water above the point of use refers to the header. (A tank in the loft supplying the bathroom below creates a decent working flow rate and pressure for the supply.)

 

[Carnegie]

Spoke to Vaillant technical re 2nd pump - they said it is possible to connect 2nd pump on system but it should be as close as poss to boiler & wire into boiler using an extra circuit board which you can buy from Vaillant & add in. However, even with 2 pumps there would probably still be a circulation problem as it is just 2 pumps 'pushing water down the same 22mm pipe'. They said the plumber who installed system should have firstly done a 'circuit index calculation' to establish what flow required which, in turn, would establish guage of pipe required to get that flow - they also said that with 25 rads the minimum, in their experience, would be 28mm, probably higher. This guage in such a large system would be fundamental knowledge to most experienced and good plumbers, as commented upon in this thread. I am now arranging for existing 22mm pipe (primary flow & return only)to be replaced by 35mm. Hopefully, the plumber who put my system in won't make the same mistake twice!! Thanks to everyone for their help.

 

[stevetheplumber]

Ive never done any calcs for pump head always rely on instinct or experience any thing very big is always designed by an engineer anyway