Posted by: @bash

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Is it better to use the LSVs to reduce the flow or let the TRVs do this?

In a word yes, its better to use LSVs, for the reasons you clearly understand.  Low flow continuously keeps max engaged volume and lowest necessary flow temp.  Its also generally more comfortable!  I found it pretty easy (and ultimately much more comfortable) to adjust the LSVs on my bedroom rads to achieve a comfortable sleeping temp whilst maintaining a higher temp elsewhere. 

However you dont have to obsess about this if it doesn't suit your lifestyle provided the majority are on LSVs- I have one exception where I use a TRV, namely a room we use principally for guests.  As a courtesy to the guest the LSV is fairly high, and they can use the TRV to turn it down.

There is an article on balancing here.  Its important not to turn down all the LSVs, at least one (normally the rad that heats up slowest) should be fully open, otherwise you are unnecessarily restricting flow.  

Thanks @jamespa 

Yes, I'd be leaving several radiators fully open with no TRVs (all the downstairs ones) and 2 bathrooms as want the most heat in these.

I'm assuming it's best to start with the bedroom closest to the incoming flow, turn that down and once happy, leave it for a day and then do the next radiator upstairs, i.e one at a time?

I'm assuming also that reducing the LSV flow in the bedrooms should push more to the furthest radiator (which incidentally is the one I want the most heat into)?

Posted by: @bash

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I'm assuming also that reducing the LSV flow in the bedrooms should push more to the furthest radiator (which incidentally is the one I want the most heat into)?

Yes

Posted by: @bash

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I'm assuming it's best to start with the bedroom closest to the incoming flow, turn that down and once happy, leave it for a day and then do the next radiator upstairs, i.e one at a time?

That is certainly what I did and what it suggests in the article I referred to.  However expect it to be a bit cyclical.  That said I found it pretty easy, probably because we leave doors to rooms open for the most part, they therefore share heat and balance is not so critical.

If you have towel rails in the bathrooms don't expect them to heat the room adequately, the output of the average towel rail is small.  Some people fit ordinary radiators or an auxiliary electric element.  We just leave the bathroom door open most of the time, so the bathroom is heated additionally from the adjacent hall.  Steam takes over when someone actually has a bath!

@jamespa 

Thankfully we'd already experienced chrome towel rails and the minimal output that comes from them and had already decided standard type 22 radiators were the way forward!

Posted by: @bash

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The house is warm and comfortable, although the bedrooms run a little warmer than the downstairs.

I'd like to push more heat downstairs and take some from upstairs to get a better balance of heat that'd we'd prefer.

Flow is what transfers heat, so when you say take heat from upstairs to downstairs, what you mean is to increase the flow downstairs by limiting the flow upstairs.

As discussed above, at the most simplistic level, you could achieve this by setting the TRVs to 18C (or as desired) which would limit the flow once the rooms are at temperature, but this is pretty much a binary on/off solution which, as you identify then limits the volume of water available to the system. So it's better to use the LSVs to balance the system if you can, but this is much harder to do accurately.

For any given heat pump, the available of flow can be proportionately split between the installed radiators. So if you have 25L/min of flow, and you have 10 equally sized radiators, you'd need 2.5L/min flowing through each radiator for them to be in balance. Knowing the different output of each radiator (for the desired room temperature), you can calculate the exact flow required to achieve that output based on the total system flow. If you have those fancy LSVs with little flow meters on, it then becomes trivial to balance the system, but unfortunately most of do not so balancing becomes somewhat of a black art with plenty of guesswork.

Your suggestion to start with one of the bedroom radiators as discussed with @jamespa above is spot on. At a practical level, I find it easiest to start when the radiator is cold, by completely closing the lockshield and leaving it for an hour or so. Then I open the lockshield a 1/4 turn (or minimum amount), just enough so I can now feel some minimal flow (heat) in the inlet pipe. Leave it for 24h and see if the room gets warm enough. If not, turn it up 1/4 turn at a time and leave for another 24h. Then move on to the next bedroom. The downside to this method is that even with the radiator completely off, the room may still feel warm enough as it's simply pulling in some heat from adjacent rooms which defeats the purpose, so I'd at least check the radiator feels warm after 24h and not noticeably cold relative to others in the house.

Thanks @old_scientist 

I was going to turn TRVs down until I got the result I am looking, but your suggestion to start form zero is a much better idea.

I am still in discussions with the installer about installing FRVs.

Had I known how accommodating they were I'd have done that before the LSVs were fitted, but unfortunately that ship has sailed.

I'm hoping that as they haven't balanced they radiators yet, due to some extra plumbing required for some old pipework to one of the radiators, they might install them without too much extra cost, else I'll have to play with the LSVs for a while after they have got them roughly ok.

Posted by: @bash

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Thanks @old_scientist 

I was going to turn TRVs down until I got the result I am looking, but your suggestion to start form zero is a much better idea.

We were extremely lucky with our system, and I've never really needed to do any balancing. With all LSVs fully open, all radiators get warm, even those furthest away, and all rooms are adequately heated.

There is a small radiator near the cylinder at centre of house which isn't really required due to the heat emitted around the cylinder/pipework, so I closed that one off and then just opened a 1/4 turn for minimal flow as it's right at the start of the circuit, helping the flow go further into the circuit. Conveniently, the furthest most radiator (which probably receives the least flow) is in the spare bedroom so is the room that needs the least amount of heat. The radiator still feels warm (difficult to tell any difference by touch as we only run 32C flow temps), as does the room, so I know it's getting sufficient flow/heat.

Those FRVs aren't cheap - around £45 each, so £500 plus labour to swap out all 11 radiators is probably going to cost you £1,000. Although I think they are a brilliant idea, I think I'd stick to LSVs or TRVs rather than retrofit them at that price.

@bash 

If you find that you cant get a fine enough adjustment on the LSVs (they can be a bit of a pain with only the last half turn making any difference) an alternative is to remove the TRV head and fit a decorators cap instead.  This then acts like a LSV but with much better control - you just use the decorators cap to adjust the flow.

@bash — another thing to be aware of is that inadvertently over-doing the lock shield tightening can reach the point where the system becomes constricted, not enough water can flow around the system. I managed to do just that, without realising it, and thereby capped my system so its max output was 1-2kW below what it was capable of producing. A very clever member of the forum spotted what was happening, and as a result I opened up all the lock shield valves fully and suddenly got the missing 1-2kW. As the rooms stayed pretty much where I wanted them with all the lock shield valves open, I just left them open. A couple of rads at the ends of runs are a bit cooler than the others but the rooms are OK.     

Thank you

@old_scientist 

@jamespa 

@cathoderay 

This is all very helpful information!

I was starting to come to the conclusion that that FRVs whilst useful, could end up being the best part of £1000 to fit and I don't really want to pay that...

What is the rough amount of flow that I'll get from the first quarter turn, would it be around half?