Radiator balancing?

[John Carlyle-Clarke]

I noticed something when trying to refill and bleed the radiators on our combi sealed system. All the rads have thermostatic valves on them. All the normal valves on the other end of the rads are fully open.

When trying to bleed them, I noticed that with all the thermostatic valves set to max, none of the rads seemed to get hot. I had to shut the thermostatic valves on all of them, and go round opening them one at a time to check the rad was getting hot and bleed it.

I can see why this would happen, but is this correct, and what should I do about it? I wonder if closing some of the tap valves on the radiators partially would improve things. I have seen mention of balancing radiators - is this what this refers to?

[Set Square]

Even with TRV, you need to balance the system - by adjusting the lock-shield valves - if you want all the rads to heat up evenly. Otherwise, some will get hot first and, only when their TRVs have closed, will the others get hot.

Do the balancing with the TRVs fully open, and with any room stats turned to max - so that the system runs continuously during the balancing operation. Measure the temperature drop across each radiator (an IR non-contact thermometer is useful for this) and progessively turn down the lockshields on the rads with the *lowest* drops until they are all more or less the same. This is an iterative process, so you'll need to go round all the rads several times.

When you're happy with the balance, return room stats and TRVs to their normal settings.

[Dave Plowman (News)]

Yup. See FAQ for details on how to do.

[John Carlyle-Clarke]

"Dave Plowman (News)" wrote in news: [e-mail]:

Will do! I think that was where I had "seen mention", but since I didn't know what it was for, I didn't read it in detail.

Thanks again to all who responded.

[Brett Jackson]

I was going to balance my raditors but couldn't be bothered in the end as they all heat up within a few minutes anyway.

Is there really any point in balancing a combi powered sealed system? Surely the fact that the boiler output generally far exceeds that required by the CH system suggests so. When I spec'd up my system the calculation gave a requirement of something like 11kw - the boiler I bought to give a good shower flow is 28kw. Maybe microbore systems are a factor as it may be more difficult to pump the water down the further reaches of the system?

[Dave Plowman (News)]

Think that tends to be the issue - one rad robbing flow from another. Also, unless you have large pipework - bigger than the 'standard' 22 mm feeding things, you won't get the full output of a large combi anyway.

[Set Square]

With *any* system with a lot of radiators in parallel, the water will take the line of least resistance. If one or two radiators are more or less resistance free, and can take most of the pump's output, other larger radiators on a higher resistance path may never get very hot. The boiler's (over-) capacity doesn't really come into it - this will never be harnessed unless an adequate flow can be got to *all* rads - the boiler will simply modulate down, or cycle on its internal stat.

[A motoring analogy would be a 4x4 car with a very powerful engine, with 1 or 2 of its wheels spinning in the mud. Until you control the wheelspin you can't harness the power].

Balancing - which means restricting the flow to the rads with the least resistance - will mean that an adequate flow of hot water arrives at *all* radiators, enabling the boiler output to be used properly.