Balancing Act

[D_Hailsham]

If the difference is, say, 20 degrees, should i be opening it to allow more flow and less of a difference?

similarly if the difference is only 5 degrees should i be closing it for less flow?

Open the LS valve to reduce difference (raise return temp); close LS valve to increase difference (lower return temp).

i tried this this morning but the problem I've found is that the difference chnges between about 5 and 20 degrees so i'm not sure at what point to take the reading.

Not sure what you mean.

Only change one LS valve at a time, by a very small amount, i.e 1/12th turn or less, and wait 5 minutes for the system to settle down. If the boiler is cutting off and then restarting, you must wait until the flow temp is back up to 75C before checking the difference.

The reason for this is that what you are doing, indirectly, is setting the flow rate through the radiator and the same flow rate will produce a different temperature drop depending on the flow temperature. For example these all have the same flow rate, within a few %:

Flow temp: 75C; Return temp 65C. Difference 10C
Flow temp: 55C; Return temp 49C. Difference 6C
Flow temp: 45C; Return temp 41C. Difference 4C

 

[StudWall]

ok, that makes sense now

so today i've started again with the lockshields all set to 1/2 a turn open, and TRV heads off. I haven't changed the pump from number 2 yet due to being banned (by the Mrs) from entering the loft for 24 hours since i put my foot through the ceiling yesterday

the first radiator i tried has an incoming temperature of 74c after the boiler had been firing for a while and it went down to about 59c then the boiler fired up again (seems to be logical to me)

at the point at which the incoming was 74 the difference was 6c so i closed the valve a bit at a time until i got the difference to be 8c, any further closed and the radiator was closed off completely ... should i turn the pump speed down?

 

[D_Hailsham]

You don't appear to be following my instructions!!

What is the boiler flow/return differential (at 75C flow)?

What is the differential at each rad (at 75C flow)?

You must have this data before you make any changes or you won't know which rad needs adjusting first.

Adjusting one rad has an affect on the other rads, which is why you have to recheck after each adjustment.

 

[St0rmer66]

And you're also wasting your time balancing now if you're going to change the pump speed later .

 

[D_Hailsham]

And you're also wasting your time balancing now if you're going to change the pump speed later.

It's a bit of a chicken and egg situation. Checking everything first will tell you if you are in the correct ball-park. Because the pump has fixed speeds you will be unlikely to get exactly a 10C drop, so you have to select the speed which gives the closest drop. Starting with the pump on speed 2 gives the maximum flexibility.

 

[StudWall]

I have the following differences at boiler flow temp of 71c (set to max):

Boiler = 14
Bedroom 1 = 15
Bedroom 2 = 16
Hall = 10
Bathroom = 7

 

[D_Hailsham]

Boiler = 14
Bedroom 1 = 15
Bedroom 2 = 16
Hall = 10
Bathroom = 7

Are those the only rads you have? What about a living room and kitchen?

If they are the only rads, I would open bed 1 and bed 2 by 1/12th turn and check again. You should find that the drop across them decreases and the drop across the hall and bathroom increases.

Post results for next instalment.

 

[MeldrewsMate]

Yes, there is a grundfos pump set to number 2.

Measuring the flow at the boiler, with the boiler set to max and the room stat all the way up, the flow pipe gets to 74 when it cuts off, at this time the return is at 56.

When it fires up again a few minutes later the flow is at 61 and return still at 56

It seems that you may have a partially blocked pump.
Isolate and dismantle the pump, and clean the impeller. With all the valves open (you only have three rads & a towel rail?) the return temperature should approach the flow temperature.
BTW if using typical type K thermocouples it's good practice to wrap insulation around them and the measured pipe, so that you get a more representative temperature.

There are many ways to balance a system, yours should be easy to do, and pump setting 2 should be perfectly adequate if the system and pump are clean.

Is the system water reasonably clean? i.e. not like mud!

 

[MeldrewsMate]

Oops, it appears in the time it took me to type my response others have helped you.
I'll back off & let them advise you.

 

[StudWall]

ok, so i've tried bedroom 2 first by opening it a little at a time then waiting for it to settle, ended up opening it by about 1/2 a turn in total and the difference didnt change at all

now i'm wondering if my temperature meter might be duff.

don't have radiator in the living room yet, there is one to add there plus one in dining room, but have a woodburner stove so that keeps them warm

the system is clean- ish, the whole thing was drained and radiators flushed last winter, i also run some cleaner and descaler through it. This year all the old radiators have gone and been replaced with new as well as the majority of the pipes being replaced.

 

[StudWall]

Think I've finally managed to solve it now and have each radiator with a 10-12 degree difference

Also when I set the thermostat to 15 in the mornings the boiler fires for a while then switches off for some time before re-firing, it's only when I turn the temperature upto 20 is it continually switching on and off in quick succession, possibly due to heat loss caused by insufficient insulation and p**s poor double glazing

 

[D_Hailsham]

Think I've finally managed to solve it now and have each radiator with a 10-12 degree difference

I certainly wouldn't try to improve on that.

What speed is the pump set to and what is the differential at the boiler?

Also when I set the thermostat to 15 in the mornings the boiler fires for a while then switches off for some time before re-firing.

But is it the room stat or boiler stat switching the boiler off?

It's only when I turn the temperature up to 20 is it continually switching on and off in quick succession, possibly due to heat loss caused by insufficient insulation and p**s poor double glazing

That will be the boiler stat turning the boiler off. Nothing to do with insulation or lack of double glazing.

The boiler is generating more heat than the rads can use, so the boiler water gets hotter and hotter until the boiler stat says, 'that's enough, time to turn off and let the water cool down'.

I would get the boiler checked to make sure it is set to the minimum output.

 

[StudWall]

i left the the speed of the pump at number 2.

the difference at the boiler is 15 degrees. The flow is 74 but at the radiators is 71 and return at radiators is 60 and boiler return is 59, the pipes are currently uninsulated so this is sort of understandable.

set to 15 i can hear the room stat clicking on and off and turning the boiler on and off. at 20 your are right it is only the boilers internal stat turning on and off, it doesn't get hot enough to deactivate the room stat at 20

 

[D_Hailsham]

Check what happens if the pump is set to 3.