Balancing Act

[StudWall]

Hello

i'm currently trying to balance my radiators having replaced them all during this years renovations, but am having a little trouble i hope someone can help with

I have replaced the old single slab rads with shiney new Kudox type 22s and fitted some TRVs. The bathroom towel radiator doesn't have a TRV and nor does the hallway (where the thermostat is, as i was advised not to)

anyways, having read many 'how-to' articles and watching some online videos about this i thought id give it a go, as my bedroom radiator wasn't getting overly hot, so i got some thermocouples from work (and a meter which can show the difference between 2 probes) attached them to the inlet pipes of the towel radiator with some tape and set to work.

As the warm water began to emerge from the boiler the meter started to show a difference between the probes getting up to 7c difference, before slowly levelling out to a difference of 0c (by this time the actual temperature of the probes was 45c) and it seemed to make fa difference whether the valve was nearly shut or fully open

i figured this was maybe because it was a towel radiator and has a very small heat output (about 600 BTU) and as such can't dissipate the heat very effectively so the water out is barely cooled at all compared to the water in.

moving on the the hallway radiator ... same problem, showing no difference between the inlet and outlet temperature, although i can feel the radiator is warm.

could someone please offer some guidance?

 

[Scarum]

Temperature difference between my first rad's flow and return is little, the lock shield is barely open and I get a high temperature.

Try fully closing the lockshield and as the system warms up open it by a few degrees at a time until you get a reading. Aim for the 12 degrees but I can only get 8 on my first rad.

Then move on to next rad in system.

 

[St0rmer66]

For the hall and towel rail they'll barely need to be open. Keep in mind that as the other TRV's close these two will get a bit more flow so even if they take a while to heat up, they'll get there soon enough. Open the lockshield just enough to hear flow through the rad.

 

[D_Hailsham]

Which boiler do you have (make and model no)?

You need a higher flow temp than 45C to balance the system correctly. 75C is more like it.

 

[StudWall]

For the hall and towel rail they'll barely need to be open. Keep in mind that as the other TRV's close these two will get a bit more flow so even if they take a while to heat up, they'll get there soon enough. Open the lockshield just enough to hear flow through the rad.

When I opened them a little (about half a turn) I can hear a huge gushing noise so I opened it a little more and it went away, perhaps that didn't help

Which boiler do you have (make and model no)?

You need a higher flow temp than 45C to balance the system correctly. 75C is more like it.

It's a potterton profile 50e. The temperature was low because I turned the boiler temp control down to 2 as one of the tutorials advised. Will turn it up and try again

 

[D_Hailsham]

It's a potterton profile 50e.

So you have a separate pump. What speed is it set to?

When the flow temp is 75C (at the boiler), what is the return temp?

 

[StudWall]

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

Measuring the flow like 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

 

[D_Hailsham]

Measuring the flow like 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

A return of 56 is too low; it should be about 65. Set the pump to speed 3 and check the return temperature again.

Remove all TRV heads and make sure the HW is turned off when you check the temperatures.

Do you have a bypass valve? If so, make sure it is closed.

If the boiler gets up to 74 then cuts off, drops to about 60 and start up again, the boiler output may be greater than the total rad output.

 

[StudWall]

I'll try turning up the pump to 3

HW is off and all TRVs are set to 5 currently (there are only 2 with TRVs and 2 without) ill also try taking them off tomorrow and trying again.

no bypass valve, i was advised i didn't need one because I have 2 rads without TRVs.

the boiler has an output of something like 11-12 kw and based on the spec of the rads i have fitted i have an output of 18779 BTU (about 5.5 kw).

Thanks for all your help so far

 

[D_Hailsham]

no bypass valve, i was advised i didn't need one because I have 2 rads without TRVs.

That's OK if you have one 3-port motorized valve, as in this pic.

View media item 5946
But if you have two 2-port valves (pic below) you need a bypass.

View media item 11762
You say the output is 11-12kW. I assume there an arrow on the data plate (inside controls cover) showing the boiler output setting. Unfortunately, with a big mismatch between boiler output and rad capacity, the system will cycle regularly.

How did you decide what size rads you needed?

 

[StudWall]

Yes I have a 3 port valve, Drayton MA1 rings a bell.

The boiler output is only what I have found from an online spec, I've not taken the cover off.

The radiator sizes were dictated by 2 things, firstly using the b&q online calculator to give me a rough idea of the btu requirement and secondly what would fit in the space, they are all of similar size to the ones which were removed, except the bathroom where there wasn't one before.


I do have another 3500 watts of radiator to fit next year but as it's turned freezing it was a priority to get the current ones working

 

[D_Hailsham]

The boiler output is only what I have found from an online spec, I've not taken the cover off.

The output is adjustable (by a qualified engineer) between 11.7 and 14.7kW. Let's hope it is at the bottom end of the range.

I do have another 3500 watts of radiator to fit next year but as it's turned freezing it was a priority to get the current ones working

That will certainly help; it might be worth doing sooner. (The boiler would still need to be on lowest output.)

Balancing
1. Remove TRV heads and set wheel valves to fully open
2. Set all lockshield valves to 1/2 turn open.
3. Get system up to temp (approx 75C flow).
4. Check the flow/return temp difference at boiler. The target is approx 10C.
5. If the difference is well below 10C, set pump to a lower speed; if well above, to a higher speed. (If possible)
6. Check flow/return difference at all rads and write them down.
7. Go to rad with the largest difference and open the LS valve by a very small amount, e.g 1/12th turn.
8 Wait 5 minutes
9. Repeat 6 to 8 until all rads have approximately the same flow/return difference (10-12C). If necessary adjust pump speed to keep difference approx 10-12C at the boiler.

Do not aim for perfection.

Replace all TRV heads and set them to the required temperature.

 

[StudWall]

ok i've taken the TRV heads off and adjusted all the lockshields to 1/2 turn open.

one thing im not sure of is how i should be adjusting it.

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?

 

[St0rmer66]

ok i've taken the TRV heads off and adjusted all the lockshields to 1/2 turn open.

one thing im not sure of is how i should be adjusting it.

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?

Correct. The amount of adjustment will be minuscule if you're trying to adjust for a few degrees though. Do not expect to get it perfect.

 

[StudWall]

thanks for all your advice!

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