Balancing Central Heating with one radiator missing

[desig]

Question is pretty much in the subject.

After buying some clip on radiator thermometers, I can see that some of the valves are open too much on some radiators (temp difference between feed and return is 1-2 degrees, rather than the recommended 12 degrees). We also sometimes have some radiators that won't heat up properly, making me think I should balance the system out a bit.

Thing is, our Master bedroom is still under renovation, and will be for a for a number of weeks. The radiator has been removed, valves are shut, and I've put blanking nuts on to make sure there is no water leakage.

My questions:
- Is it possible to successfully balance the system for now while this radiator is not connected?
- Could the missing radiator be causing me issues with air in the system, as i have previously had to bleed air out of some radiators once every few months (just wondering if the return part of the piping in the master bedroom is keeping some air in it)
- If I do balance the system, can someone explain how each valve affects the water flow? I know the lockshield valve is limiting the input flow (and the water will take the path of least resistance, allowing more water to flow to the further away radiators) but what about the TRV on the return side of the radiator? does the higher number on the TRV mean water stays in the radiator for longer to warm it up, or does the higher number mean the water flows quicker to make the temp higher?


Thanks
desig

 

[D_Hailsham]

Is it possible to successfully balance the system for now while this radiator is not connected?

No reason why you should not be able to balance the system with one rad missing. But you will have to rebalance when the rad is replaced.

Could the missing radiator be causing me issues with air in the system, as i have previously had to bleed air out of some radiators once every few months (just wondering if the return part of the piping in the master bedroom is keeping some air in it)

Have you checked for air in the flow and return to the removed rad?

The heating must be turned off before you start bleeding and the water allowed to cool down.

Bleed the downstairs rads first.

Can someone explain how each valve affects the water flow? I know the lockshield valve is limiting the input flow (and the water will take the path of least resistance, allowing more water to flow to the further away radiators) but what about the TRV on the return side of the radiator? does the higher number on the TRV mean water stays in the radiator for longer to warm it up, or does the higher number mean the water flows quicker to make the temp higher?

Normally the TRV is on the flow and the LS valve on the return. However this is not essential, provided the TRV is fitted the correct way round. Look for arrows on the metal TRV body. If only one arrow, it must point in the direction of flow (towards rad on flow; away from rad on return). This means the TRV will be upright one end and horizontal the other end. If there are two arrows, the TRV can go either end, upright or horizontal.

The purpose of balancing is to obtain the correct flow through each rad, which is done by adjusting the LS valve, irrespective of which end it is on. All TRV heads must be removed while balancing.

The numbers on a TRV head refer to the required room temperature. They are not related to the flow through the rad.

You need to check your boiler manual for the recommended temperature drop. Older, non-condensing boilers required a 10-12C drop, but many modern condensing boilers are designed for a drop of about 20C. If you can't find the info, post the make and exact model of boiler and someone will tell you the correct temperature.

 

[desig]

Thanks D_Hailsham

I have a Worcester 28i RSF, and the installation/service manual states that central heating should be balanced with a temperature differential of 11 or 14 degrees, depending on boiler output, so aiming for 12 may be close enough (as it won't be 100%)

I'll have to check the TRV's when I get home to see which ones I have. What I do know is that the TRV's are all fitted vertically on the new radiators that our builder put on (the older radiators in the part of the house not renovated have not yet been changed)

So am i right in thinking that even though there is no Radiator in the master bedroom, it would still be good to open the valves and release any air trapped in them before balancing the system?

 

[D_Hailsham]

I have a Worcester 28i RSF, and the installation/service manual states that central heating should be balanced with a temperature differential of 11 or 14 degrees, depending on boiler output, so aiming for 12 may be close enough (as it won't be 100%)

Are you referring to Table 3 in the Manual? This shows:

8kW -11C
23.5kW - 18C
27.5kW - 21C

Can't see 14C anywhere. Maybe I've got the wrong boiler. What is the GC number of yours (front cover of manual)?

11C is fine if you are running the boiler at minimum output all the time, which is unlikely unless your boiler is considerably oversized. Do you know the heating requirement of your house? If you don't, use Baxi Whole House Boiler Size Calculator.

Yes, releasing any air in the "dead legs" to the removed rad would be a sensible thing to do.

 

[desig]

Correct, table 3. The Commissioning section mentions 11-13 degrees, but references Table 3 for specifics

Boiler GC Number is: NG 47 311 54
Manual publication details were: 8 716 114 751a (11/07)

For me Table 3 has:
10.5kW - 11C
27.5kW - 14C


I tried a few combinations on the House Boiler Size Calculator, as I wasn't 100% sure on the total house dimensions. The range it gave me was between 14 and 16kW.

With all the valves open, the one radiator I still had the thermometers on shows the TRV side is 1-2 degrees lower, so I get the feeling the TRV for that particular radiator is on the return side.

Also, my (vertically fitted) TRV's have two arrows, one pointing horizontally into the radiator, and one pointing vertically down into the pipe.

My wife had already turned the heating on before I got home, so I might wait until the weekend before I embark on bleeding the dead legs and balancing the radiators.

Thanks
desig

 

[D_Hailsham]

Correct, table 3. The Commissioning section mentions 11-13 degrees, but references Table 3 for specifics

Boiler GC Number is: NG 47 311 54
Manual publication details were: 8 716 114 751a (11/07)

For me Table 3 has:
10.5kW - 11C
27.5kW - 14C

I had the wrong boiler!

I would balance the system for a drop of about 14C at each rad and the boiler. It's easier to balance a system which is running at a high temperature, say 75C.

It doesn't matter which side the TRV is on. You adjust the LS valve to get the correct temperature drop.

The valves with two arrows are correctly fitted.

Balancing
1. Set water temp to 75C
2. Remove all TRV heads and set wheel valves fully open
3. Set all LS valves to 1/3 turn open
4. Set room stat to a high temperature so boiler keeps running
5. Allow system to warm up.
6. Measure differential for all rads and make a note of them.
7a. If all rads have too small a drop, close every LS valve by 1/12th turn
7b. If all rads have too large a drop, open every LS valve by 1/12th turn
Wait 5-10 minutes for system to settle down
Repeat 6 and 7 Until some with a larger drop than required and some with a smaller drop.
8. Adjust the one with the largest drop by opening the LS valve 1/12th turn or less.
9. Wait 5 minutes for system to settle down
10. Measure drop for all rads
11a. If balance has been achieved (within +/- 1C) STOP
otherwise
11b. Repeat from 8.
12. Turn room thermostat down!!
13. Replace all TRVs and set to required temperature.
END