replacing hot water tank thermostat

Ok, here comes a really basic (ie dumb) question.... !

I think that the thermostat on our hot water tank has gone, as the water is getting scalding hot even when it is turned down low, and no matter what temeperature I select on the thermostat the water temp does not change. It is a Honeywell L641A1005 (thats what it says on the outside) and is wired into a fused spur.

If I want to change this, is it a simple case of taking the old one off and wiring the new one back on, or do I have to do soemthing else ? This seems too simple to fix like this !?

Thanks...

Yes, but first make sure you don't have an electric Immersion Heater switched on. They usually have their thermostats set high, and they fail high too.

Your Honeywell stat should be clicking as you turn it above and below the current water temperature, with quite a gap between clicks.

It's also possible that you have a 2 port motorised valve which has stuck open so is ignoring the thermostat. What have you got?

Thanks ChrisR

The immersion is swtiched off. When I turn the knob on the thermostat - which is currently set as low as possible at 50 - it does clcik and come on again when it gets to about 60..... if I turn it back down it then clicks off. However, even though it is set at 50 you cannot put your hand under the hot water as it virtually scalds you - could it be that it is working but not recognising the correct temperature ?

Our system comprises a Honeywell "Sundial Y Plan 3 Position Diverter Valve" and a Grundflos Selectric pump (both of which are being changed in 4 weeks when we get a new boiler fitted). The pump is getting incredibly hot when the water is on (so hot you can hardly touch it - is this normal ? I've never notice before, but then again haven't tried to touch it before) so I dont know if this may be contributing ?

Thanks...