Help with uneven heat in new replacement radiator

[Haveagohero]

I have just swapped out a single panel radiator for a double in our cold bathroom. I have bled the system out and confident that the system is as free of air as it can be. On starting up (heating both water and radiators), the new radiator was a little slow to heat up and when it did it wasn't as warm as I'd have expected and only warm at the top and inlet side. All other radiators were fine.

The next morning: the programmer is currently set just to heat hot water, when the hot water (only) is on this radiator is also heated - that's the way it is setup. Interestingly, when just heating the hot water the new radiator gets very hot - as I'd have expected - and also evenly.

A friend of mine has suggested the balance has gone out of synch with the system, so I have started to look at resetting the balance and here I have more problems....

I was told that in most systems the radiator lockshields downstairs are most likely to only be open a half to full turn and the upstairs is more likely to be almost fully open. Well, all my lockshields are fully open except for one - which oddly happens to be the last radiator upstairs! Which also happens to be one of the hotter radiators i have.

Also, in trying to suss out the order in which the radiators heat up, I have found this really difficult and have two downstairs and one upstairs that I really cannot figure which order they heat up - they are all pretty much together when they get warm.

I would really appreciate guidance in first diagnosing that balancing is the likely problem and in how to suss out the problem of the order in which they heat up and just how critical is it to balance in the right order.

Sorry I know this should be handed over to a professional but unemployment dictates that I must struggle with it myself!

 

[stevetheplumber]

just shut down as far as you can on each rad to allow it to still work yourr bathroom rad is fed from the primaries to the cylinder it may be on gravity so will work slower than rest

 

[doitmyself]

I was told that in most systems the radiator lockshields downstairs are most likely to only be open a half to full turn and the upstairs is more likely to be almost fully open. Well, all my lockshields are fully open except for one - which oddly happens to be the last radiator upstairs! Which also happens to be one of the hotter radiators i have.

If all the LS valves are fully open, either the system has not been balanced or you have TRVs and the installer thinks that systems with TRVs don't need balancing - wrong.

Also, in trying to suss out the order in which the radiators heat up, I have found this really difficult and have two downstairs and one upstairs that I really cannot figure which order they heat up - they are all pretty much together when they get warm.

It can be difficult to work out the order. You need a person at each rad feeling the flow pipe. Start with the system cold and shout out as soon as you feel any warmth in the pipe!

It is much easier to balance if you know the order.

Balancing the hot water circuit, which in your case also includes the bathroom rad, should be done as part of the balancing. Otherwise the bathroom can hog all the flow.

Read How to balance a CH system

 

[Haveagohero]

Thanks for the info guys, I really need it!

If I can bore you a little longer, I have found the following using a digital thermometer all temps in centigrade, in the order I think they warm up - 3 are very difficult to suss. I did one reading, amde minor adjustments then another:

First test
Hall: 65in 54out
Living1: 63in 53out
Living2: 58in 58 out - turned down lockshield half turn
Bed3: 63in 55out
Bed1: 64in 53out
Bed2: 65in 60out turned locksheild quarter turn
Bath: 63in 37out

Second Test
Hall: 67in 57out
Living1: 66in 55out
Living2: 64in 57out
Bed3: 58in 58out turned down lockshield half turn
Bed1: 64in 58out turned locksheild quarter turn
Bed2: 64in 58out turned locksheild quarter turn
Bath: 64in 41out

This is all done with boiler at highest temp and room thermostat (hall) on highest.
Am I going in the right direction with this? I have switched off the heating an allowing to cool down and will take another set of readings later

 

[doitmyself]

If I can bore you a little longer, I have found the following using a digital thermometer all temps in centigrade, in the order I think they warm up - 3 are very difficult to suss.

Are you using an Infrared thermometer? If so you need to be aware that the reading can vary considerably with the type and colour of the surface they are pointing at. To give consistent results you need to wrap some black insulating tape round each pipe and measure the temperature off the tape.

The typical lockshield valve does not have a linear flow characteristic, i.e you do not get half flow when it is half open. In fact most LS valves are giving full flow when they are about 1½ turns open. For that reason it's better to start with all valves closed and open them a bit at a time to give the correct drop. See the link I posted earlier.

 

[Haveagohero]

Hi
Thanks for the info once more.
I did read the link you posted after I had started!

One thing, I wasn't going into this totally blind, I had a read a balancing DIY guide from another site and on that site there was a very clear suggestion that all locksheilds would be on the return side of the radiator in fact this is what they say: ".... you will adjust the lockshield valve to create a flow differential of around 11 degrees cellsius - the lockshield valve is normally covered and situated on the return side of a radiator..."

Some of my locksheilds are on the flow (input) side of the radiator, does this make any difference to the way I go about balancing? I'm thinking by starting with all lockshields closed, then if the lockshield on the flow side is closed, opening it will let hot water in not cool water out... or am I getting myself even more confused?

Also to add that I am using infra red thermometer with tape over the target pipe

 

[doitmyself]

Some of my lockshields are on the flow (input) side of the radiator, does this make any difference to the way I go about balancing?

It does not matter which side the LS valve is. All you are doing is adjusting the flow through the rad. The slower the flow, the greater the temperature drop across the rad. Commercial installers balance their office block systems by having flow meters situated at critical points in the system. This is overkill for a domestic system so the temperature difference is used instead.

If you do not have TRVs on the rads, you may be able to swap the LS cover with the wheel handle. The valves are normally identical, just different tops.

I'm thinking by starting with all lockshields closed, then if the lockshield on the flow side is closed, opening it will let hot water in not cool water out... or am I getting myself even more confused?

You can't take instant measurements, even with IR thermometers, as it takes time for the temperature to stabilize after you have adjusted a LS valve. Probably best to wait at least 5 minutes after making an adjustment before taking the temperature.

It can be a long slow job!

 

[Haveagohero]

All radiators except bathrrom and hall have TRV's.
Yes does seem a long job.... I'll have another bash at it later or perhaps tomorrow

 

[fuzzy]

if bathroom rad doesnt have a trv then it obviously wont be the issue. i suspect it is the last on the loop and gets heat last, maybe being starved of heat by unbalanced system. maybe blocked ports on valves, not vented correctly.

what size is the rad and what size is the pipework? are there any other rads of the same pipework?

 

[Haveagohero]

This is the radiator I swapped out. The original was a single 700x500 which was rusting due to small leakwhere the lockshield connects and the bathrrom was never well heated by this little rad, so I got a 700x500 P+ double radiator and also purchased new valaves as I thought it might be a false economy not to.

I think it is the last in the loop. I have no idea if any other rads are on the same pipework, all I know is that there is a connection between this radiator and the heating of the hot water because whenever the hot water is on, so is this radiator, which kind of suggests it could be separate to the main heating circuit. It's not easy for me to say with my limited knowledge of this subject.

What do you mean by 'not vented correctly'?

 

[WHPES]

Could be connected to the hot water circuit which goes to the cylinder - this is quite common for heated towel rails. Did the radiator work during the summer when the heating was off?

Also be aware if your cylinder is controlled by a thermostat - when the cylinder reaches temperature, it will shut the radiator off too.

 

[Haveagohero]

Yes the radiator is ALWAYS on with the water - even in summer, but not a problem in the bathroom.
No thermostat that I know of on the cylinder and the water has been known to get T-O-O hot!

 

[stevetheplumber]

is your system fully pumped if not the balancing of the heating circuit will have little effect on a rad fed by gravity

 

[Haveagohero]

As far as I know it is fully pumped - how can I tell if the bathroom isn't?

 

[WHPES]

If it isn't fully pumped, the pump will only go on when the central heating is required.

Firstly, do not touch any of the valves or lockshields on the rest of your radiators - they are on a different circuit.

Did you reuse the old radiator valves or did you fit modern ones? For gravity, you need valves and lockshields suitable for gravity heating systems.

 

[Haveagohero]

Pump seems quiet when heating water at the moment, but I'm sure I hear it kick-in when programmer first switches on... I'll have to check
No bought new B&Q valves - just standard valves they can be used with wheel or as lockshield

What is the difference and what difference to balancing if the water and new rad is gravity fed?

I forgot to mention earlier the pipework is 15mm

 

[Haveagohero]

OK ripped up the floors and placed a glass of water on the pump then got she-who-must-be-obeyed to switch on the water - the pump was quiet, no vibration through the water in the glass - so I think we can now assume that what I have is a gravity feed to the hot water and thus to the bathroom radiator.

So does that mean that it is a completely separate circuit from the main room radiators and balancing them will have no effect on he bathroom?

WHPS: I have been searching the web for valves that are specifically for gravity systems but none seem to mention what system they are for - how do I tell which are suitable?

Finally where do I go from here? trying to get a good flow of heat in my bathroom radiator when the heating is on?

 

[doitmyself]

OK ripped up the floors and placed a glass of water on the pump then got she-who-must-be-obeyed to switch on the water - the pump was quiet, no vibration through the water in the glass - so I think we can now assume that what I have is a gravity feed to the hot water and thus to the bathroom radiator.

Another trick is to use a screw driver or metal rod as a stethoscope (one end against the pump, the other in your ear).

How many pipes are there connected to your boiler (ignore the gas pipe)? If more than two, you have a pumped heating, gravity HW system.

So does that mean that it is a completely separate circuit from the main room radiators and balancing them will have no effect on the bathroom?

If it is a gravity HW, balancing the rads may have an effect on the bathroom rad. This is because balancing the rads could make mean the pump can be run at a lower speed, which makes more flow available to the gravity circuit. You need to balance the rads in any case as it obviously has never been done.

I have been searching the web for valves that are specifically for gravity systems but none seem to mention what system they are for - how do I tell which are suitable?

The pipes on a gravity circuit are normally 28mm, so 15mm valves will create a significant restriction. That's why the towel rails in old houses were made of scaffold-pole sized chrome pipes with valves to match.

15mm TRVs are no good on a gravity circuit. Danfoss make TRVs specifically for gravity circuits.