Radiator not getting hot

[JohnD]

if you turn off all the hot radiators, does the cold one then warm up?

if so, it is most likely because there is an easy passage of flow through the hot one(s).

If there is an easy path, them the hot water will tend all to go through there, especially if it is closest to the pump, it will circulate through the path of least resistance........

etc

etc

 

[merton69]

Latest test....

I have just turned on the CH and the cold rad is now hot (not as hot as the other rad though) still minus the TRV and one of the hot rads was cold!

I took off the TRV on the cold rad and became hot but again not as hot.

 

[D_Hailsham]

All lockshields are fully open.

So I don't have to repeat myself,

Did you reset the lockshield valves to their original positions? No?

Then the system needs balancing

Read How to balance a CH system.

 

[cbucket]

Perhaps I can answer (and others can elaborate).

You essentially have to open the lockshield valves (output) more or less depending on how close they are to the pump. So lets say you have 10 radiators. You would open the nearest one 1/10 of its full amount, the second one 2/10th, the third 3/10ths etc.... and the 10th one fully open.

Thats my understanding of it (but the link given, above, probably explains it better). Basically, if you dont do this the radiators nearest the pump get all the flow, and hence get hot, and the ones further away dont get much/any flow and hence remain cold.

 

[D_Hailsham]

You essentially have to open the lockshield valves (output) more or less depending on how close they are to the pump. So lets say you have 10 radiators. You would open the nearest one 1/10 of its full amount, the second one 2/10th, the third 3/10ths etc.... and the 10th one fully open.

How far you open the LS valve is related more to the output of the radiator. This is because you are trying to regulate the flow through the rad and the flow is directly proportional to the output.

If you have a 20kW boiler the flow rate, assuming an 11C differential will be 26.1 litres per minute (20 x 60)/(11 x 4.18 ). A 1kw rad needs a flow rate of 1.30lpm and a 2kW rad needs 2.61lpm.

So you have water belting along a 28mm pipe at nearly 30 lpm and it comes to a 15mm branch. The flow rate through the branch will slow down because of the reduced size of the pipe and the increased friction, but there will still be about 7kW of heat travelling along the 15mm pipe at a flow rate of 9lpm. So if you have a 1kW rad attached to the 15mm pipe you have to reduce the flow rate to 1.3lpm, i.e it has to be reduced by 85%.

This explains why LS valves are frequently almost closed on a properly balanced system.

The typical LS valve is actually giving maximum flow when about 1½ turns open. So, in our example above the LS valve would have to be only about a quarter turn open.

 

[merton69]

One question please.

I have an Ariston EuroCombi boiler on my CH.

Can the pump on these get weaker or do the either work or don't work (break down completely)?........as I feel the flow seems to be struggling to get around the system.

Thanks,

 

[JohnD]

what has happened to make you suspect that to be the cause?

how old are the radiators?

 

[merton69]

The whole set up is about 10 years old.

The reason I am querying the pump is because before the initial cold rad trouble started, the LS's haven't been touched since installation.

Then all of a sudden since the trouble started, I am being instructed by various people on here to adjust them.

At the moment 2 of the 3 upstairs rads are without the tower valves and heating okay.

The downstairs rad (the initial problem rad) is struggling to reach the same temperature again.

The 3 upstairs rads are first in the flow down to the 2 downstairs.

Please forgive me if this is getting long winded, but right now I can't call a CH man in because I am unemployed with a family of two young kids, so I am trying to sort it myself.

 

[D_Hailsham]

Lets go back to the beginning!

You have six rads and one is not getting hot.

Was it OK last year?

 

[merton69]

Thanks...

..all six are getting hot...BUT....the double rad is not getting as hot as the others.

The original problem was the double rad downstairs wasn't getting hot at all.

 

[D_Hailsham]

all six are getting hot...BUT....the double rad is not getting as hot as the others.

The original problem was the double rad downstairs wasn't getting hot at all.

I asked if you had this problem last year?

It could be that the TRV is stuck (the pin still move).

Remove the head and tap the body of the valve with a hammer. This may free the valve..

Are the LS valves still fully open?

If yes to both, close all LS valves and then open them all half a turn. Test the system. If a rad is too hot, close the valve very slightly; if the rad is too cold, open the valve slightly.

 

[merton69]

None of the TRV's are stuck/damaged. All been checked okay, as with the pins.

No I did not have this problem last year or since the CH was installed.

The LS have not been altered since installation.

 

[JohnD]

The LS have not been altered since installation.

so they might be wide open

 

[JohnD]

I can't believe we're still saying this

All lockshields are fully open.

that'll be the trouble then.

 

[merton69]

I can't believe we're still saying this

All lockshields are fully open.

that'll be the trouble then.

Yes, you are!

Your answer of "That'll be trouble then" is little help, sorry!......please elaborate?

As far as I am aware the LS are open, but like I said before...the CH has been like this since the installation 10 years ago and not had one problem with it until now!