Does my Central Heating system need to be balanced?

[xyza]

I understand the desired differential between flow and return at each radiator is 10-12C for a standard (not combi) gas central heating system. The difference in flow and return temperatures at each of my radiators is considerably lower than this. It varies between a difference of 2C (lowest) and 7C (greatest).

Although all of my radiators get hot should I be balancing them to achieve the 10-12C differential at each? What would be the effect I would feel of changing to the higher differential? Would it be a more consistent temperature?

Also the lockshield valve appears to be on the "higher temp" pipe on some radiators but on the "lower temp" pipe on others - is this normal or have the flow & return to some of these somehow got reversed?

 

[denso13]

Is it warm enough, are you comfortable enough? If so, don't worry about it and leave thing as things as they are.

 

[Happyplumber]

All heating systems should be balanced correctly to run a efficient system

 

[Madrab]

As happy says, it's the difference between a system that keeps you warm and a system that keeps you warm and running at max efficiency.

 

[D_Hailsham]

I understand the desired differential between flow and return at each radiator is 10-12C for a standard (not combi) gas central heating system.

The important differential is that at the boiler. Older non-condensing (and some condensing) boilers were designed for an 11C differential. Modern condensing boilers have a 20C differential. I think you might be getting confused between combi (instant hot water) and condensing.

The difference in flow and return temperatures at each of my radiators is considerably lower than this. It varies between a difference of 2C (lowest) and 7C (greatest).

Measuring the temperature differential is indirectly measuring the flow rate through the rad. The smaller the differential the higher the flow rate and vice versa. If the differential is only 2C, flow rate is over five times faster than it should be. This results in greater friction in the pipes, so the pump has to work harder (higher setting) to move the water round the circuit.

1. Although all of my radiators get hot should I be balancing them to achieve the 10-12C differential at each?
2. What would be the effect I would feel of changing to the higher differential?
3. Would it be a more consistent temperature?

1. Yes
2. You may be able to turn the pump down, saving electricity
3. If you mean consistent room temperature, probably not. TRVs and a room stat with TPI control are needed for that.

Also the lockshield valve appears to be on the "higher temp" pipe on some radiators but on the "lower temp" pipe on others - is this normal or have the flow & return to some of these somehow got reversed?

Its 'normal' to have the LS valve on the return (lower temp) but it doesn't really matter. If you have TRVs on your rads there's not much you can do - unless you want to swap them over! But if you have standard wheel valves you should be able to just swap the wheel head and the LS cap and the job is done.

How to balance
Detailed instructions see How to balance a CH system

Quick method
Check Boiler Manual for correct differential (post boiler info here if the data not available).
Remove all TRV heads and open wheel valves fully.
Shut all LS valves then open each one a quarter turn.
Let the system settle down then measure the differentials.
Open the LS valve 1/12 to 1/8th turn if the differential is too high; close the same amount if too low.
Let it settle down then recheck.
You may have to go round several times and the pump speed may need to be lowered (if possible - depends on boiler).

Don't try to achieve perfection - a few degrees either side of the target will be good enough

 

[xyza]

My terminology was wrong (sorry), it is an older non-condensing boiler.

The differential at the boiler is 12C.

The radiators heat up quite quickly (approx. 15-20mins to get to between 70-75C), however the room temperature does not heat up in the same way - it can take up to 3hrs to warm the house up and get to temperature on the room stat (21C). It's almost as if the heat in the radiators is not being distributed back into the room - is this possibly because the flow is too fast?

Also there seems to be no control of the room temperatures once the house is heated - rooms temperatures are totally variable, some remain just warm and some continue to heat up and get over hot. (There is 1 central room stat on the landing and where TRVs are fitted these are all set to max).

I will try to rebalance by following your useful advice as soon as I get time to do it. Thanks.

 

[doitall]

Sounds like you'd be better spending on some better insulation for the property, or shouting at the kids to shut the damn door.

 

[D_Hailsham]

it can take up to 3hrs to warm the house up and get to temperature on the room stat (21C). It's almost as if the heat in the radiators is not being distributed back into the room

So the heat is escaping from the room almost as fast as the rads can produce it. That's a rads size/poor insulation problem. Improved insulation the one to go for as a well insulated house will save you money on the heating bills.

Also there seems to be no control of the room temperatures once the house is heated - rooms temperatures are totally variable, some remain just warm and some continue to heat up and get over hot. (There is 1 central room stat on the landing and where TRVs are fitted these are all set to max).

Who put the stat on the landing? The normal place is in the hall or the living room.

Why set the TRV to max, is it because the rooms don't get hot enough? If so that's due to the problem above, i.e. rad size/insulation. Turning the TRV to max will have no effect.

Rebalancing may reduce the variability between rads, but it sounds as if they have not been correctly sized for the heat loss.

Come back when you have balanced the system.

 

[xyza]

Sorry its taken so long to get back. I had (unsuccessfully) tried to balance the radiators previously then other matters prevented me following through.

However having now had a determined effort to get a grip on this I discover that it is impossible to change the differential at the radiators no matter how closed or open the LSV. In fact at times, on some radiators, the return is (briefly) higher than the flow. All differentials are low (zero to 8C). Flow & return temps are all around 70-75C (peaking at 80C).

I have measured temps going into and out of all components within the system (ie pump, 3-part valve, Aerjec) and these are also the same (approx 70-75C, peaking to 80C), this (worryingly?) also includes the 2 pipes from the Aerjec into the F&E tank in the loft. (However the water in the F&E tank in the loft is cool to the touch – it is noted that when Ferinox was added 2 years ago this tank had a “scum” floating on the water until recently – its as if the water in the tank has been totally replaced ).

I have also observed the boiler as the house heats up. All rads get to between 70-75C within approx. 15-20mins but the boiler then switches off, continually switching on and off for only 1-2mins at a time. The flow / return differential at the boiler when only CH on is approx 7-8C (pump on 2). (With the pump on 1 the differential is about 9C, pump on 3 about 6C).

My problem is the house taking such a long time to heat up and there seeming to be no control of the room temperatures once it is heated.

Does all of this point to a flow problem? Is it likely to be in the system or in the boiler?

It has been suggested previously in this post that I could have poor insulation / incorrectly sized radiators but I don’t believe this to be the problem as, prior to my last boiler service, the house was always very comfortably warm.

Could the engineer have altered something in the boiler to cause this problem? (Prior to him checking the burner pressure he commented upon how he “wished people would leave settings alone”. What other setting could be referring to?) The Boiler is a Baxi Solo WM 30/4 RS

It seems as if the boiler stat, rather than the room stat, is now controlling the heating? (probably because the water returning to it is now too hot?).

Any help to try to get this problem resolved would be more than appreciated.

 

[JohnD]

I discover that it is impossible to change the differential at the radiators no matter how closed or open the LSV.

After you had closed the lockshield on a radiator, what fraction of a turn did you open it? A half? A quarter? An eighth?

My problem is the house taking such a long time to heat up and there seeming to be no control of the room temperatures once it is heated. .

Taking a typical room, let's say your bedroom:

What are the dimensions of the room?

Are the wall 9" brick, 13" cavity, or cavity insulated? How old is the house?

What is the area of outside wall? Is the wall 9" brick, 13" cavity, or cavity insulated? How old is the house?

How thick is the loft insulation? Is it gappy?

What sort of window have you got, and what size?

What are the dimensions of the radiator?

What is the temperature of the radiator?

What is the outside temperature?

What is the room temperature after the heating has been on for an hour, with the bedroom door closed?

When you bleed the radiators, what comes out?

 

[xyza]

LSV opened 1/2 turn = no change, 1/4 turn = no change - no making so much noise not really wanting to take it any lower.

Bedroom = 310x320x230

Cavity insulated. 25years old.

Loft insulation 20cm all over (& boarded)

Double glazed window 170x110

Radiator = 80x50 double

rad temp = 75C but then drops to cold as boiler switches off then back up to 75C, etc

I have already done close monitoring of inside & outside temp in parallel = initially 18.7C in, 5.5C out. 1hr later = 19.2C in, 7.4C out. 1hr later = 19.9C in, 8.4C out. 1hr later = 21.2C in, 10.7C out. 1hr later = in 21.9C, out 13.0C (Stat is set to 22C). The outside temp rises at a faster rate than inside with heating on.

Bleed rads = clean water coming out immediately (ie no air).


I still do not believe it is down to poor insulation / incorrectly sized rads as it had previously got up to temp, even on the "coldest of mornings" within approx 1/2hr (being really warm well within the hour and remaining that way throughout the day). It used to get to temp on the room stat before the boiler stat turned it off. The rads remained "comfortably warm" throughout rather than the current very hot / cold. I believe the reason it is now taking so long to heat up because the boiler stat is switching it off and on for such very short intervals. Any ideas why the boiler is now behaving in this way?

 

[D_Hailsham]

prior to my last boiler service, the house was always very comfortably warm.

Could the engineer have altered something in the boiler to cause this problem? (Prior to him checking the burner pressure he commented upon how he “wished people would leave settings alone”. What other setting could be referring to?)

He could have changed the boiler output - it can be set between 6.15 and 8.79kW (21,000 - 30,00 BTU).

Do a Gas Rate (see How much gas am I using) when the boiler is working flat out. This will give you the input to the boiler.

Because a boiler is not 100% efficient the output will be less. Here's the data for your boiler:

Minimum: 8.01kW Input = 6.15kW Output
Maximum: 11.27kW Input = 8.79kW Output

As the problem has only arisen since the boiler was last serviced it might be a good idea to ask him:

Did he change the boiler output?
Why?
What is it now set to? (Compare with your measurement )

 

[xyza]

By "boiler output" do you mean Burner Pressure? If not what is boiler output and how do I check this?

I'm aware he changed the burner pressure. It had always been 14.2mbar but he changed it to 15.6mbar (he told me the reason for this is because the pointer on the boiler indicated 15.6). He could not remember what else he had changed.

As I was immediately getting problems after his visit I requested he return and reset it to 14.2mbar. At that point I tested the gas rate and it was 10.34kW

When this did not resolve the issue he convinced me it was because the pressure was now too low (although it had been 14.2 for years!) so it was reset as a compromise to 15mbar. Again I tested the boiler input which was 10.12kW (why was it lower now that the burner pressure was set higher?)

You suggest I compare boiler output with my measurement - how do I do that as I'm measuring input?

In the "How much gas am I using" FAQs it states "Be aware that if the boiler can't get rid of its heat fast enough, it might well "modulate" which means turn itself down.". It seem this is the problem I'm experiencing (ie the boiler now can't get rid of its heat fast enough) - what could be the cause of this for my standard boiler?

 

[D_Hailsham]

By "boiler output" do you mean Burner Pressure? If not what is boiler output and how do I check this?

Boiler output is the number of kW of heat it can put into the water to heat it up.

Boiler input is the number of kW which the gas supplies to the boiler. This varies with the gas pressure.

Because the boiler is not 100% efficient the output is always less than the input.

I'm aware he changed the burner pressure. It had always been 14.2mbar but he changed it to 15.6mbar (he told me the reason for this is because the pointer on the boiler indicated 15.6).

15.6mbar is the maximum setting, equivalent to 11.27kW Input or 8.79kW output.

THe problem is that the boiler is preset to max output, even if the house does not need it, and the original installer must have turned it down a bit but not bothered to put this into on the data plate. Hence your chap's comment about someone changing things.

[As I was immediately getting problems after his visit I requested he return and reset it to 14.2mbar. At that point I tested the gas rate and it was 10.34kW

That's about right; the reduced pressure will mean a lower heat input/output.

You suggest I compare boiler output with my measurement - how do I do that as I'm measuring input?

Forget that, you have already made the necessary comparisons

In the "How much gas am I using" FAQs it states "Be aware that if the boiler can't get rid of its heat fast enough, it might well "modulate" which means turn itself down."

Only modern condensing boilers modulate - automatically adjust their output. Your boiler has a fixed output, which is set when installed by adjusting the gas pressure. When it is firing it runs at the preset full output, so the only control you have is to turn the boiler on and off.

This is done by either the boiler thermostat (when water reaches set temperature) or by the room thermostat.

The boiler could be providing more heat than the rads can use.

How many rads do you have, what type and what size?

 

[JohnD]

I'm wondering if there is a bypass.