Radiator thermo and lockshield valves

[shantondiy]

I have a lpg combi boiler supplying 10 radiators. The central heating system is of a two pipe design.
All of the radiators are fitted with a thermostatic valve and a lockshield valve.
I am familiar with the method to balance radiators using thermometers with a supply and return system and adjusting the lockshield valve to achieve the difference in temperatures flowing in and out of the radiators.
I do not now how I should be setting the lockshield valves on my system where the flow out on the two pipe system goes back to the boiler and not on to the next radiator.
With the frightening cost of lpg I'm keen not to burn more gas than I need.
Thanks

 

[D_Hailsham]

I do not now how I should be setting the lockshield valves on my system where the flow out on the two pipe system goes back to the boiler and not on to the next radiator.

Not sure what you mean. Ignoring pumps, motorized valves etc the basic two pipe system looks like this:

Two pipe

• D_Hailsham
• 19 Oct 2008
• 1

Basic two pipe layout

If you can knock up a diagram in Paint it would help.

 

[Slugbabydotcom]

I do not now how I should be setting the lockshield valves on my system where the flow out on the two pipe system goes back to the boiler and not on to the next radiator.

My translation is this:-
You know how to balance a one pipe system but not a two pipe system.

With the frightening cost of lpg I'm keen not to burn more gas than I need.

Nobody likes paying more than they have to for heating. Its a good job that you have TRV's to help keep the costs down.

The purpose of balancing a system is to keep all the rads at a fairly even temperature so that all rooms that need heat can be heated evenly. Balancing rads is only really an issue if you have some rads that dont heat up enough to warm up a room. By reducing the flow to rads nearer the boiler there is more available for the ones further away. On a one pipe system the last rad will always be cooler but with a two pipe system its generally less of an issue.

You can go to the fine end of a fart balancing a system monitoring temp drops across the rads etc. but don't forget that the end product is simply to provide adequate heat to a given airspace. Simply having and using TRV's will take care of most of it so don't be having big headaches as in your case accurate balancing has little relation to how much gas you use.

 

[shantondiy]

Slugbabydotcom has got the gist of my "long way round" post. I was concerned that inadequate/incorrect balancing would be reflected in an increase in fuel usage. There isn't an issue with regard to some radiators being cooler than others.
The diagram shown by D_Hailsham pretty much shows my system if you add another seven rads as the pump is included in the boiler.

Cheers

 

[D_Hailsham]

The purpose of balancing a system is to keep all the rads at a fairly even temperature so that all rooms that need heat can be heated evenly. Balancing rads is only really an issue if you have some rads that dont heat up enough to warm up a room.

Radiators need water flowing through them at a specified rate and with a specified temperature drop to produce their rated output. If a radiator is not giving the correct output, the room will not reach the required temperature and the TRV will stay permanently open.

By reducing the flow to rads nearer the boiler there is more available for the ones further away.

It's not a matter of reducing the flow but of providing the correct flow. A 1kW radiator next to the pump needs exactly the same flow as a 1kW radiator furthest from the pump.

Simply having and using TRV's will take care of most of it

That's plumbers folklore! Why do you think so many people complain that the TRVs are not working? The system is not balanced correctly

Balancing procedure:

1. Turn boiler off and allow to cool
2. Make sure HW is turned off
3. Open all LS valves fully; remove all TRV heads and open all manual rad valves fully.
4. Turn the boiler temp to max and bring system up to temperature.
5. Check, by feel, the order in which the rads warm up and make a list.
6. Adjust the bypass (if fitted) as per mfr instructions
7. Measure the temperature differences between the flow and return pipes at the boiler. What it should be will depend on the boiler -refer to the installation manual. If the temperature is not right, you need to adjust you pump speed (higher speed gives smaller difference and vice versa). Set the speed to give as a difference as close to the mfrs recommendation as possible.
8. Turn the boiler off.
9. Close all lockshield valves. Leave TRV heads off.
10. Restart boiler
11. Attach the pipe thermometers to the first rad in the list made in step 5 and open the LS valve a quarter turn
12. Wait until temperature has stabilised on the two thermometers. If the difference is smaller than that at the boiler, close the LS valve a fraction, or vice versa. Wait until the temp has stabilised and check again.
13. When you are happy with the first rad, move on to the next on the list.
14. Repeat steps 11, 12 and 13 for each rad on the list.
15. When you have reached the last rad, check the boiler temp difference and adjust pump speed if necessary.
16. Go back to the first rad and test it is still giving the correct difference
17. And so on, going round and checking the temperature difference until they are all as near the required drop as you can make them. Don't expect perfection
18. Replace TRV heads and set to required temperature

if you do not have clip on thermometers you can use an infrared thermometer (about £25 from Maplin)

A very small change in the amount a LS valve is open can have a considerable effect on the temperature difference. Because of the way LS valve are constructed, it is virtually fully open when it is one and a half turns open. So most adjustment will be within one turn from closed.

If you find that the wall thermostat is turning the boiler off before the TRVs in the other rooms work, you should close the wheel valve slightly, so the rad gives out less heat and the room/hall warms up slower. It's a matter of trial and error.

 

[shantondiy]

Thanks for the very comprehensive explanation and set of instructions.

I'll need to get a thermometer(s) and dig out the installation instructions before I start. As I said in my last post though, I'm not getting a problem with cool radiators or cold rooms. I just want to be sure the boiler is working as economically as possible.
Thanks