Testing a Thermostat in a boiler...

[whazza22]

Hi,

Could someone tell me the best way to test a working thermostat and high limit thermostat to ensure it is working correctly?

Im assumming a multimeter is best option.

Thanks

 

[malcolmsanford]

Is it calibration or just if the stat is just functional.

Calibration would be hard to check on without actually testing water temperature and making allowances for drops over a system.

A simple way to check your operating stat is isolate the supply and let the tank run cold overnight say. Then next day turn the stat down to the lowest setting.Then turn it up until you hear it click and turn on the electric supply. You can then check for voltage on both sides of the stat until it clicks off/voltage would be off on the load side. Then ratch it up again till you hear it click and so on.

As for the hi-temp or limit stat I personally would not try that on your system. If you can remove the stat from your tank, after isolating the electrics then wire out the control stat with a small piece of wire, and in your kitchen boil a kettle and pour the water into a pyrex bowl and immerse the stat in the boiling water, this should be hot enough to activate the hi-limit stat.

 

[Piratepete]

A simple way to check your operating stat is isolate the supply and let the tank run cold overnight say. Then next day turn the stat down to the lowest setting.Then turn it up until you hear it click and turn on the electric supply. You can then check for voltage on both sides of the stat until it clicks off/voltage would be off on the load side. Then ratch it up again till you hear it click and so on.

As for the hi-temp or limit stat I personally would not try that on your system. If you can remove the stat from your tank, after isolating the electrics then wire out the control stat with a small piece of wire, and in your kitchen boil a kettle and pour the water into a pyrex bowl and immerse the stat in the boiling water, this should be hot enough to activate the hi-limit stat.

I'm slightly dubious about this. New thermostats come with a blob of sealant on them preset at 60 deg. If it is sealed, it's unwise to twiddle it! I would use the hi-limit stat test method. You'll need a thermometer and connect your meter (on min Ohms range) across the terminals. Heat it up slowly and see that it opens around 60 degC. The high limit stat (i'm assuming it's an integral one) should operate (you can see it pop up) at about 85 degC. On the one I just bought you can't wire out the control stat.

Pete

 

[malcolmsanford]

Thanks Pete fair enough, I can't remember the last time I fitted a cylinder stat to be honest, the last one I did still had the little arrow indicator that you dialled up and down as you wished.