Balancing problem

[marsaday]

I have a balancing problem and wondered if i could turn up the pump to pump a bit harder. It will be set on std factory setting.

There is no blockage in the system, just that the rads dont get fully hot all the way to the bottom. I have tried to balance it as best i can and can't get a better result. All the rads are new in the last 2yrs.

The boiler is on the attic level, feeds 11 rads and 1 UFH loop. It is a big boiler - vaillant 937 and is approx 35kw.

The system has been power cleaned 3 yrs ago and recenlty i have added a new floor to the house (attic) and so now have 3 new rads up there. Because the boiler is up there i just ran the piping in 15mm for this level. The rest of the house is 22mm.

I know i have one problem spot and that is the flow/return to my bed rad in the attic. they have to go over a steel beam and then back down again so here i have a section of pipe which goes up / across / down. It did it in elbows because i couldnt bend the pipe to give smooth corners. This rad needs about 2 1/2 turns to come on where as the other 2 rads only need a 1/4 turn as the boiler is so close. So i know this rad is pinching some flow from the rest of the house, but i would have thought it wouldnt distort the rest of the system that much.

I haven't tried shutting this rad down yet, but i might try.

Do you think upping the pump power will do the trick ?

 

[dcawkwell]

You could well be reaching the limit of what one pump can do.
Usually about 14 or 15 radiators over two floors.

You have the additional problem that the boiler is the attic and you
are pumping over 3 floors with UFH.

Does the underfloor heating have it's own pump and blending valve?

I would try cutting off the underfloor and balancing the radiators.

 

[D_Hailsham]

The boiler is on the attic level, feeds 11 rads and 1 UFH loop. It is a big boiler - vaillant 937 and is approx 35kw.

That's a very big boiler for eleven rads and a UFH loop. Presumably it was selected for its hot water capability.

1. Does the boiler keep turning on and off so it takes a long time to get up to temperature?

2. Did the installer say anything about "range rating" the boiler so it gives of the correct amount of heat for the rads and UFH?

If the answer to 1 is 'yes' or 2 is 'no', that needs to be put right first.

Use Whole House Boiler Size Calculator to find the heating requirement of your house. Treat the loft conversion as an extra floor, the same size as those below. Deduct 2kW from the result as you have a combi boiler.

This gives you the heating requirement for your house. If it is considerably lower than 35kW, the boiler output needs to be reduced. How this is done is explained in the installation manual; it's parameter d.0. You can do this yourself.

 

[marsaday]

Hello thanks for replies.

Yes the UFH has its own manifold and pump. There are 2 port valves by the boiler to switch on the UFH when it is needed.

The boiler is big so i dont think this is a problem.

I remember now the engineer on a service did turn down the power of the boiler because it didnt need so much and since then i have added the new floor and 3 extra rads. So i think the solution is to turn up this "rating"

I have the manuel and can do this no probs.

 

[marsaday]

I have done the heat loss calcs and the kw demand is 22.

It was 15 before i converted the attic and i remember the boiler output is set to 16. So all i need do is increase to 22.

Do you think i could make it a little lower as the attic is simply 2 sloping roofs and so half the volume of a regular floor. Also it has been very well insulated to 125mm kingspan.

The boiler is doing ok with it set on the lower setting so i am pleased about that.

I will try aim for 20kw i think.

 

[D_Hailsham]

If the boiler is set to 15kW and you now need 20-22kW, the boiler will be running flat out all the time in a vain effort to produce enough heat. This is the exact opposite of what I originally suggested! This would explain why the rads are not getting hot all over.

Accounting for loft conversions is difficult as the online calculator does not allow for this. If you needed 15kW for two floors and 22 for three, then the average is 18.5kW. I would start there and increase if necessary.

The calculator assumes an outside temperature of about -3C, so you may find that you need the boiler set slightly higher in the current very cold weather.

 

[snb]

firstly i would alter the adjustable bypass within the boiler. Set it at maximum.(turn clockwise all the way in usually takes about 4 to 5 turns)

See if this solves it before adjusting other settings