radiators getting TOO HOT

[BluesCon]

Hi

I have a Baxi Bermuda boiler and, after it has been on for about an hour, the bathroom radiator has been getting very hot. It is the only radiator without a thermostat. I turn the thermostat, mounted on the boiler, down to LOW but still the radiators are too hot. There are no other problems with the system and the temporary solution is just to switch the heating off for a while till things cool down. There is no knocking sound to indicate a faulty pump etc.

I'm guessing that the boiler thermostat is faulty. Is there any way that I can test it? Is it easy to replace?

thanks for your help Nigel

[Grunff]

I'm not familiar with your boiler, so won't comment on it (I'm sure someone who is will be along shortly). But as for the radiator, how about turning down the lockshield valve?

[Malc]

It might not be the boiler stat. How hot is too hot by the way? If you turn your boiler stat way down it's still going to be kicking out water at 60 C or more (I've never actually measured it so I don't know) which can feel very hot to the hand. As Grunff suggested turning the valve down might be a better solution. If your boiler stat was faulty and overheating you'd probably get kettleing, which you'd hear.

-- Malc

[Set Square]

Is there a room thermostat, mounted on a wall, somewhere? If not, there should be - to turn the whole lot off when all rooms are up to temperature.

If the boiler stat is working, it should cycle the burner on and off every few minutes - unless the weather's so cold that the boiler needs to run flat out to keep up. The best way to check it is to measure the temperature of the water flowing out of the boiler. This is best done using a non-contact IR thermometer, pointed at the outlet pipe. This should be somewhere between

70 and 80 degC depending on the thermostat setting.

If the boiler stat *is* faulty, it's not *too* difficult to replace. You need first to remove the gas fire, in order to get at the boiler controls. You can *probably* replace the stat without disconnecting the boiler controls and sliding them out from under the heat exchanger - I can't remember exactly since it's a long time since I owned one. The thermostat assembly is a little box with a knob and a couple of electrical connections - and a capillary tube with a bulb on the end, which has to be inserted into a pocket at the top of the heat exchanger.

[BluesCon]

Thanks for the responses. We have had this system for 14 years and this problem only started around 6 months ago. The lockshield valve's have not been adjusted in this time so I dont feel that this is the root of the prob. I will keep it in mind, thanks.

There is no room thermostat, never has been. I just use the boiler stat to adjust the overall tempoerature.

The burner appears to be staying on all the time and not cycling on and off. It will go off when I turn the boiler stat down to LOW but otherwise appears to stay ON. I will check this again before posting back. I'm away for a few days so may not post back on this till the weekend.

[Set Square]

It's important to check the flow temperature then. You just *could* be using the entire boiler output without the water temperature ever getting hot enough to turn the stat off.

One other thing to check that is that the bulb of the thermostat is making good contact with the heat exchanger. I seem to remember that there's supposed to be some sort of paste in the pocket to ensure good heat transfer.

[BluesCon]

Problem fixed, thanks for all your help. It turned out to be the thermostat after all. I tried reseating the thermostat bulb initialy but to no avail. A new thermostat has seloved the issue. Although I had reconned on this being faulty from the beginning your help and advice helped confirm my suspisions. Cheers