Help with uneven heat in new replacement radiator

[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.