Feed and return pipe size

[proppi]

Hello,

I need some advice from the experts please.

As part of a full refurbishment of our house we had a completely new heating system installed: Vaillant Ecotec Plus 630 system boiler (30kW), three heating zones (loft = 2.5kW total radiator output, first floor = 6kW, ground floor = 10kW) plus a 210l hot water cylinder, new heating pipes and radiators everywhere.

The plumber has fitted a 22mm gas pipe from the meter to the boiler (distance is around 6m), 4 zone valves (3 heating zones plus hot water tank - S style) with a 22mm pipe between the boiler and the valves. Immediately after the valves the feed pipes are downsized to 15mm for all three heating zones.

Having the heating system up and running now it turns out that the first floor and loft radiators get hot but some of the ground floor radiators don't. The plumber claims that the first and loft floor radiators are getting all the heat effectively reducing the amount of heat available for the ground floor. To prove his point he shut down the valves for first and second floor which improved the situation on the ground floor but still not all radiators get properly hot. He is now suggesting to add a pump to the ground floor zone.

My thoughts and questions are:

(1) The boiler should be powerful enough to heat all three zones simultaneously (30kW boiler for 18.5kW of radiators plus hot water cylinder) even without the help of an additional pump. Am I asking for too much here or should this be possible (which would imply that the plumber did not design the run and size of the heating pipes correctly)?

(2) 15mm feed and return pipes on the ground floor seems too small for 10kW of radiator heat output, I would assume these should be 22mm. The plumber will probably not be keen to change this as some part of it is running in new screed (the largest part is running in the void underneath the house though and the floorboards are still open). Is adding an extra pump a reasonable solution to the problem (assuming it will solve the issue of the radiators not getting hot) or should I insist on the feed and return pipe being upgraded to 22mm on the ground floor?

Thanks for your help!

 

[joni os]

15mm pipe will struggle to carry 10Kw, but it only needs replacement in part with 22mm, so each 15mm run serves not more than 5Kw of radiators.

 

[tamz]

If anything the ground floor will need 22mm to at least the 1st branch off depending how it is piped.
Rule of thumb is 6kw max for 15mm but that is dependent on lengths of runs and can be a bit higher.
Tell him to read the boiler book as there are a couple of things that can be altered that will give improved flow rates.

 

[SimonG]

For some reason 13,500 btu springs to mind for 15mm. Been a long time though.

 

[tamz]

Depends on a lot of variables Simon but 20000btu keeps the water slow enough to avoid noise.
You could double that easily if you speed it up and buy earplugs lol

 

[SimonG]

I can't even remember why that number was stuck in my head.

 

[tamz]

Probably just one of those numbers someone told you one time.
10mm is on its limit at 13000

 

[SimonG]

Not a fan of 10mm, especially when a diyer taps a new rad into an existing 10mm supply.

 

[SimonG]

Back to the op though. Is there only one pump? I like to fit a pump per zone.

 

[Gasmk1]

what size pump has he fitted ?

 

[tamz]

Its an ecotec system boiler. The pump and bypass needs set up properly

 

[joni os]

In answer to the OP:-
1. It appears the pipe size calcs, ( If done.) were incorrect. Confirmed by rads not heating.
2. Calcs for ground floor pipe work should be reappraised and 15mm replaced with 22mm as
required.
Depending on layout, it may be possible to accept 15mm pipe in screed, although if pipes are to be replaced damage to existing is not a problem.
A system boiler shouldn't require an additional pump, for 18.5Kw heat load off 30Kw boiler.

 

[Last Plumber]

As above the pipe sizing being corrected should solve it.

If he does decide to put an external pump in on that boiler, it will need a low loss header.

The boiler has a pressure sensor that detects the increase in pressure from the pump starting. External pumps can cause issues with that in my experience.

It is also the recommendation by Vaillant

 

[proppi]

Many thanks to all of you for your useful advice.

The plumber has agreed to replace part of the ground floor pipes with 22mm so that we should not be left with more than 5kW on a 15mm run.

He decided to also add a pump to the ground floor zone. After reading the post from Last Plumber I am now wondering whether he did more good or bad with this. I will have to check what kind of pump he has used (and obviously check if the radiators now all heat up properly).

 

[joni os]

Provided 15mm limited to 5Kw the pump could prove an unnecessary complication.

 

[proppi]

If it does prove a complication, can I just turn it off?

 

[Last Plumber]

depends how its wired in but if you can turn it off then yes