Radiator Balancing Query

I have just moved into a new house, switched the central heating on and it not working properly.

Radiators
We have 7 upstairs radiators and 9 radiators downstairs.
All radiators are fitted with TRV and Lockshield valves

We have underfloor heating one additional room

Boiler
Boiler is a Worcester Condensing Boiler Model- Z8-728 recently serviced
Rad temp dial is set to 4 out of 6
Display is reading 62 degrees
Eco light is on
Pressure is approx 1.5 bar

With the upstairs thermostat on 30C and the boiler on permanently I can not get all of the radiators hot.

If upstairs lockshields are open so the rads are hot then the downstairs will be cold.

When upstairs rads are turned down so they are warm (not hot) I can get all of the downstairs rads warm except 3.

If I switch all of the upstairs and the majority of the downstairs rads off I can get the three problem radiators hot.

But as soon as I start to introduce more than a couple of other rads into the circuit these go cold again.

I have tried to balance these by touch so all of the rads feel like they are at the same temperature rather than use thermocouples as I don't have any. But I have had to turn the radiators down so they are between 1/4 and 1/2 turn on at the Lockshield value.

I haven't tried to adjust them so that there is a 12C difference between input and output as I think this will take too much heat out of the water flow upstairs and will lead to cold rads downstairs - plus I don't have thermcouples.

I believe the pump is set to 3 and is working.

I have tried to increase the pressure in the system further but the input water feed won't take the pressure higher than 1.5.

What do you suggest next?

Increase the temp further and try and rebalance?

Invest in a set of thermocouples and set each rad to 12C each (I am very sceptical that this will work)

Any advice appreciated

Phil






When all other rads are switched off I can get these very warm

Phil, it depends on the location of the radiator and its pipe run from the boiler, i.e first rad on the pipe run to the last (if you know). It also depends on whether your system is clean, no sludge build up in pipework or rads, if any of the valves are partially stuck closed, if the pump is operating fully with no airlocks in the system, etc. Proper way is to get 2 thermometer straps, attach them to the flow and return pipework on the rad, and adjust the lockshield, with the TRV fully open, to get a 10 degree drop in temp from flow to return. Most guys work through the system, the nearest rad to the boiler having its lockshield partially open, right throuogh to the furthest one, lockshield fully open. Also, check the bypass valve isn't open too much. Hope this helps.

Another thing, DO NOT increase the system pressure to anything above 1-1.5 bar. This is the normal operating pressure of a sealed system in a 2 storey property.

open all the lock shields fully and set the trvs to your preffereed choice.
turn the heating on as you've described leave for 15 mins then note which are the hottest and coldest rads,
close the lockshields on the hottest rads ubtil they are about a third of a turn open leave for another 15 mins, closing the hottest (until one third open) until thier all at a simier temp.

might take more than one go but you'll find which are the hottest and coldest rads and by adjusting the lockshields you'll crack it in a couple of hours max..

Thanks for the advice

don't worry I can't increase the system pressure which is probably a good thing.

I have just discovered a separate pump on the underfloor heating which I have just slowed down as I think the underfloor heating system may have been robbing the rest of the central heating system.

I don't think any of the valves are stuck as I have managed to shut the rads of using both the TRV and the LS valves.

The house has been extended and I cant figure out the rad sequence. Is there an easy way to work it out?

Also what temp difference would you expect between the boiler flow and return pipes as they both feel very hot?

Where would I find the bypass valve?

How can I check for an airlock?
I thought the fact that all rads got hot independently eliminated this.

Thanks in advance

totalshell

If tried setting all lockshields so the rads hit the same temp (warm not hot) with the TRV fully open and the result was 3 cold downstairs rads.

Do you think that the method you suggest will give a different result?