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JamesI, Handyman
Category: Appliance
Satisfied Customers: 2085
Experience:  I have repaired and maintained numerous items over the years, from fridges to freezers, radios to TV's.
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I have an existing rmt230 room thermostat connected to the

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I have an existing rmt230 room thermostat connected to the mains by three wires. Blue to term4 black to term1 and red to term 2.Ihave purchased a TP5000si mains only thermostat and have noted that there are 3 connections N L and earth.What do I do with the existing black wire?

Good afternoon my name is ***** ***** will assist with your query today.

Please give me a minute to look up you specific model of thermostat.

Looking at the wiring diagram here for your RMT230, both terminal 4 (blue) and 2 (red) are neutral\common, which is a strange colour coding, and would be inclined to use a multi meter to double check, that only black is your live.

When wiring a different type of thermostat such as the TP5000 you would normally look to run two pairs of cables, as I think you will run into issues otherwise.

As stated earlier the TP5000 has two sets of terminals; mains (marked by L and N) and a switched - which activate the boiler (marked 2 and 3), on the old thermostat the switch pair was terminals 1 and 2, so after checking with a multi meter you know Black is live from the boiler, I would jumper the Live (black) from the Live terminal L, to that on terminal 3 (switched live), then place the red cable in terminal 2.

Good morning do you still require assistance?

Customer: replied 1 year ago.
hi James used multi meter as suggested. Results as follows Voltage across term4 and1=0. voltage across term1&2=0. Voltage across term2&4=0. In desperation went out and bought a volt test screw driver. when inserted into term4,term1 and teem2,all glowed red suggesting that all cables are live. this cannot be correct. HELP

Can you send me a link to the type of screw driver as some of them arent up to the job, some measure electromagnetic field.

My suggestion would be to set the multi meter to continuity then check you have continuity across the terminals 1 and 2 of the old thermostat, activate the thermostat and check its making and braking the circuit.

The next thing to check is when you manual jumper terminals 1 and 2 together does the boiler start, and when you break them apart does the boiler stop.

Customer: replied 1 year ago.
hi James.The volt test driver is a cheap one costing £2.50 from B&Q .Regarding the old thermostat it stopped working hence the new one. What are the likely consequences if I assume black to be the live and connect the new thermostat as previously suggested

Well based on the wiring diagram I have for you old one I cant see how the wires can be anything different (unless there are two versions of the same model).

What I would do is just focus on the switched terminals as mentioned above and check if you connect the wires in terminals 1 and 2 together if the boiler runs, and if you disconnect them the boiler stops, if it does this tells you everything you need to know to go with the wiring suggestion I made at the start.

Worst case if you cause a short, is you could blow the PCB as you end up pushing mains current the wrong way in a PCB, a new PCB is upwards of £150, so you really want to be sure, best case you probably just blow the fuse in the PCB.

Customer: replied 1 year ago.
hi James,have disconnected cables from terms1&2 boiler still on.Have not tried connecting 1&2.while disconnected I used my cheap volt tester and found that RED was live. Does this tell you something. Have traced cable to junction box in airing cupboard and found that the earth was connected[not at thermostat] and the blue wire was not connected and taped off with green &yellow tape. Look forward to your reply.

Right so in essence your thermostat has two wires (the blue in term 4 is disconnected, at the other end so can be ignored).

With this known your setup is as per figure 5 in the manual referenced here. If the boiler is running could it be because you have the boiler set to continuous\bypass, otherwise during the boiler wouldnt be working at all as the thermostat was faulty?

We need to get in a position where we can get the boiler in a idle situation with Red and Black disconnected, so when you connect them the boiler starts, this proves everything is in place as we can then use the black and red for the switch side of the new stat (terminal 2 and 3).

Customer: replied 1 year ago.
hi James, success at last. Many thanks for not only your very thorough technical knowledge but also your patience in helping a 77 year old ignoramus. My rating would be 10 out of 10. Thanks again and goodbye.

Glad we got everything working, appreciate if you click on the 5 star rating so I may close the case.



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