CEntral Heating & Thermostats

[amudda]

Hi all,

Quick question, just to make sure I'm not going mad!

I have just moved into a new house - it's got a boiler in about 10 years old, with a British Gas UP1 programmer, and there is a thermostat on the wall in the hall - a REALLY old Honeywell one, with the temperature in fahrenheit - it seems to make clicking sounds at about the right places, though.

Am I completely correct in thinking that, if I set the thermostat to, say 45 Fahrenheit (ie a very low temperature, much lower then the ambient temperature) and turn the heating on at the controller, the boiler shouldn't actually fire, because the thermostat should be telling it not to?

Because the boiler does fire, and the thermostat setting doesn;t seem to make a difference. Am I missing something, or can this only be either

a) thermostat is broken
b) thermostat isn't actually connected

Any advice appreciated before I look at fitting a new stat!

Cheers,

A

 

[simond]

It could be a duff motorised valve so don't buy a thermostat just yet.

To answer your next question you need a multimeter or at least a mainstester screwdriver to test the stat.

 

[amudda]

Sounds fun I have a multimeter, what am I testing for?

If I turn the heating off at the programmer, it does go off, so I am assuming the motorised valve works - if I understand it correctly, the programmer controls the valve, and the thermostat informs the programmer - so if I can use the programmer to have hot water only or hot water/central heating, the motorised valve is ok - the problem is that the thermostat isn't telling the valve when to shut off heating (or the boiler when to stop firing and the pump when to stop pumping) - is that right?

 

[Agile]

That may be what you think happens but it does not work like that !

The programmer, via the thermostat, powers the motor valve and when that opens it powers the boiler and pump.

If it sticks open then the boiler will stay on!

Tony

 

[amudda]

Ah OK - but, if I turn the heating off manually at the programmer (by setting it to OFF), the heating does go off - and, when I have the programmer set to Hot Water ON, Central Heating OFF, I do only get hot water, not heating as well - does it sounds as though the motorised valve is working? - i.e. I can have hot water OR central heating OR both OR neither, as I select them on the programmer - I just can't get the thermostat to turn the heating off

 

[bengasman]

It does sound like the stat is gone, but measuring is knowing.
Turn off the electricity at the spur for the boiler.
Take the cover off the stat.
Check with multimeter that there is no electricity on the stat, measure between every possible combination of any 2 wires, with stat all the way to the right, and all the way to the left. Pay no attention to the colour coding; lost of stats are wired wrong.
If no voltage anywhere, do the same combinations but now on resistance; if the stat works, you will see the meter change on at least one combination of wires when you move the stat.
If it doesn't change, stat is dead.