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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3632
Experience:  Heating and Controls engineer
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My Potterton Room Thermostat has failed. Model PRT100. The

Resolved Question:

My Potterton Room Thermostat has failed. Model PRT100. The existing wiring on this thermostat is: Blue wire to Terminal 1 (TL); Red to Terminal 2 (H), and Yellow to Terminal 3 (N). Unable to purchase a direct replacement I purchased a Honeywell T6360B Thermostat which only allows the following connections: Live to Terminal 1, and Neutral to Terminal 2 OR 3 depending on switching current. I am left with the RED wire (currently identified as H for HEAT I believe) spare. Honeywell couldnt offer any assistance. Have I purchased the wrong thermostat, or do I no longer require the RED wire?

Submitted: 3 years ago.
Category: HVAC
Expert:  Andrew Smith replied 3 years ago.

XXXXX XXXXX :

Red and yellow should be the switching wires with the red being live.

XXXXX XXXXX :

Blue should be for the netral

XXXXX XXXXX :

So 1 and 3 for live and switched live and 2 for the neutral

Customer:

So from what you are saying, my thermostat has been wired incorrectly by the engineer?

Customer:

So to clarify:

XXXXX XXXXX :

If you turn the heating on at the programmer can you tell me what colour wire is live?

Customer:

terminal 1 is live - so is this TL or H symbol? I realise that wiring colours are not standard, so just need to know what connections I require. My old blue cable is connected to TL whatever that is, and Red to H, and Yellow to N.

XXXXX XXXXX :

The live should go to terminal one on the new stat.

XXXXX XXXXX :

Switched live to 3

XXXXX XXXXX :

and neutral to 2

Customer:

I assume that blue is live as its connected currently to TL, terminal 1. Red is connected to H

XXXXX XXXXX :

Are you able to test them with a meter?

Customer:

OK, I think I have it, but just wonder why there are 2 neutral connections on this stat. There is one for loads of 10A (Terminal 3) and one for loads under 6A (terminal2). Doesnt that mean I'm using the neutral twice? I somehow think this thermostat is the wrong one.

Customer:

I have a meter

XXXXX XXXXX :

Ok take the wires out of the stat and tell me which one is live when the heating is on?

Customer:

OK. will be a couple of minutes

Customer:

Blue is 240v

XXXXX XXXXX :

The plumber should be shot!

XXXXX XXXXX :

Blue to 1 then

Customer:

So we know blue is live. Yellow is neutral

XXXXX XXXXX :

Now we just have to find out which one feeds the motorised valve for the heating

XXXXX XXXXX :

If yellow is neutral then that goes in 3

XXXXX XXXXX :

Which leaves the feed for the heating in 3

XXXXX XXXXX :

SORRY NEUTRAL IN 2

Customer:

So I am left with red which is the switched live?

XXXXX XXXXX :

1 and 3 link for heating on, 2 is the neutral on a Honeywell

Customer:

So thats all I need to wire the room thermostat

XXXXX XXXXX :

yes

XXXXX XXXXX :

whats left?

Customer:

Thats it. I can piece this together now.

XXXXX XXXXX :

Ok, no problem - come back if you need me

Customer:

Thanks.

XXXXX XXXXX :

Is it working correctly now?

Customer: I purchased a different 3 wire thermostat and made the connections suggested.
Customer: All worling
Customer: thanks
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