Removing Old Thermostat

Ben1989

Hi all,

I’ve decided to start the mammoth task of removing the artex which is ALL over the house. I’ve had it tested and it contains no asbestos.

There is an old thermostat which seems to do nothing to the boiler. However, I am not electrically minded and have no way of knowing if it is live. Is there an easy way to check? I have absolutely no clue where the wire goes.

If it is not live, how would I go about removing the wire? Any advice?

Thanks in advance.

grumbler

Ben1989 said:

There is an old thermostat which seems to do nothing to the boiler. However, I am not electrically minded and have no way of knowing if it is live. Is there an easy way to check? I have absolutely no clue where the wire goes.

What sort of boiler and and with what controller/programmer do you have? How do you control the temperature if this thermostat "seems to do nothing"?

Normally room thermostat is connected either to a box near a hot water cylinder or directly to the the controller and one wire can be live.

If it is not live, how would I go about removing the wire?

You must make sure that the wire isn't connected on the other end to anything. In this case you can just cut it.

Jeepers_Creepers

As Grumb says, what actually controls your CH temp at the moment? And, trace that wire and find out where it goes - it'll most likely be either to where the boiler is located, or to where your hot cylinder is - if you have one.

Ben1989

So the house used to have a hot cylinder but now we have a combi-boiler. The temperature is controlled from a timer or there is a temperature ‘level’ dial. It’s a Worcester greenstar 28i junior 

Section62

grumbler said:

If it is not live, how would I go about removing the wire?

You must make sure that the wire isn't connected on the other end to anything. In this case you can just cut it.

With huge emphasis on the "isn't connected" part.  Being part of a control circuit, the fact it isn't live at any point in time doesn't mean it isn't in use and/or could become live at a different time.

The other end of the cable needs to be located - proven to be the same cable - then both ends need to be appropriately dealt with, which should include labeling so the next person knows what they are.

Just cutting off the thermostat end risks the cable becoming live at a later time, or someone doing fault-finding at a later date discovering the other end disconnected/loose deciding it needs to be reconnected to something.


Also, some thermostats have a neutral connection. So cutting through the wire in one go could trip an RCD somewhere, even if the cable isn't live.


I'd suggest for safety reasons that this isn't a job for someone who isn't electrically minded. It involves proving the safety of disconnection, not just hoping it will be Ok.

Ben1989

Thanks for your replies.

What is a good method of finding the other end? I don't exactly want to be lifting floorboards up etc.

Section62

Ben1989 said:

What is a good method of finding the other end? I don't exactly want to be lifting floorboards up etc.

Without the right test equipment, proving the other end of the cable will probably require floorboards to be lifted as you'll need to follow it by sight from one end to the other.

A professional with the right kit will be able to find the other end and prove it, only needing to lift floorboards if the other end is hidden under them.

I would advise either leaving the thermostat connected, or else get a suitably qualified electrician to investigate and disconnect safely.

NSG666

Ben1989 said:

Thanks for your replies.

What is a good method of finding the other end? I don't exactly want to be lifting floorboards up etc.

Sounds like you have a programmable thermostat for the combi boiler. With the old stat shown turned right down, turn on the heating using your timer and putting the temp up to 28deg. If the boiler fires up the heating then it's a fair assumption that the old thermostat has no function. If the boiler does not fire then turn the old stat up to max and if it then fires the old stat is still needed.

Once you've established the old stat isn't needed the safest thing would be to check whether it's live using a meter such as 
LAP AC/DC Digital Multimeter 600V | Multimeters | Screwfix.com

Once tested that it's not live cut the wires at the floor and poke them under it.

ONLY DO THIS if you feel safe and competent to do so.

Section62

NSG666 said:

Sounds like you have a programmable thermostat for the combi boiler. With the old stat shown turned right down, turn on the heating using your timer and putting the temp up to 28deg. If the boiler fires up the heating then it's a fair assumption that the old thermostat has no function. If the boiler does not fire then turn the old stat up to max and if it then fires the old stat is still needed.

Still a fair assumption if the thermostat has nothing to do with the central heating and was installed for some other purpose?

No. A potentially dangerous assumption.

If the thermostat was made redundant by a competent boiler installer then it should have been removed or marked as out of use. If the boiler installer wasn't competent then the thermostat could still be live with only the control wire disconnected. Or any other combination of dangers.

If the thermostat was part of the CH system, then as the installer hasn't removed it or marked it, what might that say about the competence of the installer?

The OP will be taking a dangerous risk by making any assumptions here.

NSG666 said:

Once you've established the old stat isn't needed the safest thing would be to check whether it's live using a meter such as 
LAP AC/DC Digital Multimeter 600V | Multimeters | Screwfix.com

So if the thermostat is supplied by a timer or other control device which is off when the OP does the test? What has the test proven?


There's a lot of electrical jobs that a novice can safely do with helpful tips from people on the internet... but this isn't one of them.

NSG666

Section62 said:

NSG666 said:

Sounds like you have a programmable thermostat for the combi boiler. With the old stat shown turned right down, turn on the heating using your timer and putting the temp up to 28deg. If the boiler fires up the heating then it's a fair assumption that the old thermostat has no function. If the boiler does not fire then turn the old stat up to max and if it then fires the old stat is still needed.

Still a fair assumption if the thermostat has nothing to do with the central heating and was installed for some other purpose?

No. A potentially dangerous assumption.

If the thermostat was made redundant by a competent boiler installer then it should have been removed or marked as out of use. If the boiler installer wasn't competent then the thermostat could still be live with only the control wire disconnected. Or any other combination of dangers.

If the thermostat was part of the CH system, then as the installer hasn't removed it or marked it, what might that say about the competence of the installer?

The OP will be taking a dangerous risk by making any assumptions here.

NSG666 said:

Once you've established the old stat isn't needed the safest thing would be to check whether it's live using a meter such as 
LAP AC/DC Digital Multimeter 600V | Multimeters | Screwfix.com

So if the thermostat is supplied by a timer or other control device which is off when the OP does the test? What has the test proven?


There's a lot of electrical jobs that a novice can safely do with helpful tips from people on the internet... but this isn't one of them.

Fair points Section and probably best left alone but what else do you think it could be for? (Genuine question not trying to be clever with you)

I've seen loads of these left in situ when the CH system controls have been changed probably because the old stat is less ugly to look at than the 'gap' in the decorating if removed or they just couldn't be bothered. I guess there must be lots of incompetent installers out there.

Ben1989

All fair points. The thermostat has ZERO effect on the heating. However, I couldn't even hazard a guess where the end of this stat could be. The tanks were in the loft if that's a possible old use.