radiator valves

[panasonic1]

We have just had valves fitted. Bulldog they have numbers 1 - 5 on them. Are these called thermastatic valves.

 

[Puddle]

Yes they are good quality termostatic valves, made by pegler,the higher the number,the higher the temp before they close,if you have just had them fitted,surely installer explained

 

[doitmyself]

Yes. The numbers represent room temperatures, 3 or 4 will normally be the correct setting. You just set the valve to a number and the room will be maintained at the temperature represented by the number.

 

[panasonic1]

Thanks for that, how exactly do they work, do they turn off if the room is warm. sometimes the radiator is very hot sometimes cooler. think it should have been explained better to us. I have the conservatory one on five, others on 4

 

[Puddle]

Well inside head there is a small wax cartrige that expands as air increases in temp and contracts when air temp decreases this pushes a plunger up and down at the bottom of the head
the head is connected to the valve body that opens and closes by a pin going up and down through the top of valve body
when you put head onto valve body ,head plunger fits above body pin
when you put setting to 1 you are setting head plunger close to body pin therefore slight expansion of wax cartridge/temp rise will close valve,if you set to 5 you are increasing distance between head plunger and body pin thus more more expansion of wax cartridge/higher temp requied to close valve
When you feel radiator,sometimes hot,sometimes,warm,sometimes cold,this is because the valve closes when temp reached,when you feel rad and only warm,it does not mean warm water is now going through rad,,it means rad is cooling down as valve closed,as required air temp has been reached

 

[Bernie2]

They usually work by sensing air temperature in the head, which expands a bellows and pushes down on a pin to close the valve.

The problem I find with them, is that they sense the temperature only about 150mm away from the rad and in some rooms it may be hot 150mm away from the rad, but it isn't 2 metres away. So people turn them right up to the highest stop, which can kinda defeat a lot of the thermostatic action of the valve.

 

[doitmyself]

Just couple of observations.

A TRV does not work as a switch, turning the radiator on and off. It is a modulating control which adjusts the flow of water through the radiator so the heat produced by the radiator matches the heat lost from the room. If the radiator is continuously getting hot and then going cold, it is a sign that something is wrong. Assuming the radiator is the correct size, the problem is nearly always due to the system not being properly balanced.

Secondly, most of the better TRVs now use a liquid or a gas, not wax as the sensing medium. The reason for this is the slow response time of wax compared to liquids and gas, typically 40 minutes for wax and 20 minutes for liquid/gas.

 

[johnsco]

If the room is large, then the control from one TRV may not be adequate to keep the room temperature as you wish.
You need also to consider whether two or more rads are required in a large space ... Especially a large open-plan living room

 

[panasonic1]

so if hall thermostat is set to 25 when these radiators reach that temp they go off, and come on when room cooler again. do any thermostatic radiators have thermostats on other than numbrs 1 - 5

 

[doitmyself]

so if hall thermostat is set to 25 when these radiators reach that temp they go off, and come on when room cooler again.

Not quite right. Lets say the TRVs are set to 20 and the hall thermostat to 25. The rooms will heat up and when they reach 20 the TRV will close down just enough to maintain the room temperature at 20. The hall will carry on heating until it reaches 25, at which point the thermostat opens and turns the boiler off. Both hall and the rooms then start to cool down. The boiler will not come on again until the hall thermostat closes. The drop in temperature will depend on the type of thermostat. Very old mechanical ones had a temperature difference of 4 or 5 degrees; modern mechanical stats have a differential of about 2 degrees. The latest digital stats, which use a temperature sensitive resistor to measure the temperature, have a differential of between 05. and 1 degree.

Normally you would not have the hall stat set so much higher than the rooms. The correct setting will have to be found by trail and error -start with the stat set high, so the TRVs work, and then reduce the stat by 0.5 degree at a time until the TRV can no longer maintain the room temperature. Then put the temp up 0.5 degrees.

do any thermostatic radiators have thermostats on other than numbers 1 - 5

No manufacturer makes TRVs with actual temperatures on them. The reason for this is that each heating system is different and so is each room. One room may require the TRV set to 3 to maintain a temperature of 20, another room may need the TRV set to 4 for the same temperature.

 

[doitmyself]

The radiators were not very hot, just looked at the boiler and the temperature on radiators? was not set at maximum which they recommend for winter months.

Presumably you mean the the boiler's central heating temperature?

 

[panasonic1]

Yes, there are two dials one for water and one for radiators, in the book says turn to maximum for winter, it has done the job. Also the valves that were fitted when we turned them right down to 2 there was no heat on the radiator now there is. Thanks for all help. its ok me doing that is it

 

[doitmyself]

Yes, there are two dials one for water and one for radiators, in the book says turn to maximum for winter, it has done the job.

That's fine. I would leave it on max all the time. The hall thermostat will control the boiler and in the summer the heating will not be on.

Also the valves that were fitted when we turned them right down to 2 there was no heat on the radiator now there is. Thanks for all help. its ok me doing that is it

You set the TRV to have the room as warm as you want. If setting it on 2 is OK, that's fine. If you are too cold, try a higher number.