0

I just replaced my old thermostat and timer for a Google Nest, but every time I turn the electricy back on, it goes off shortly after. I have an oil boiler for heating.

Before I call an electrician, what could be the problem? How can I troubleshoot it?

I'm looking for guidance more than for a straight answer if that's possible.

Thanks!enter image description hereenter image description hereenter image description here

Antonio MG
  • 101
  • 1
  • 4
  • 2
    Are you referring to a breaker at the panel or a breaker in the heating system? Either way, what was the thermostat you replaced? How many wire system do you have? Did you run a common wire? The NESTs instructions come with a series of alternative-situational wiring schemes you follow. Also, wire color is NOT always correct, so it is best to verify the colors and the connections at the control board side **the furnace side. What could be wrong? You wired a current carrying wire to a neutral/common. – noybman Aug 20 '17 at 14:25
  • 2
    Post pictures of what you changed, maybe someone can suggest specifically what to test. It appears you've created a dead short. – Tyson Aug 20 '17 at 14:26
  • 2
    Oh - you also mention "thermostat AND timer" did you replace two things? Please tell us what they were, and ideally, their model numbers – noybman Aug 20 '17 at 14:27
  • 2
    Can you post photos of the thermostat wiring at both ends? (t-stat end and furnace end) – ThreePhaseEel Aug 20 '17 at 14:35
  • 1
    Please add photos as @ThreePhaseEel notes. Definitely want to see what you are working with behind those components. What is under that rectangular panel? Also, while it appears you have it hooked up "the way it was", does it work? Would be good to ensure there isnt something ELSE tripping the breaker – noybman Aug 20 '17 at 14:43
  • Added photos, the timer has 3 cables (1 2 3) that were connected to the nest using the attached scheme – Antonio MG Aug 20 '17 at 14:43
  • Behind the rectangular panel was a themorstat that I removed, leaving only the timer – Antonio MG Aug 20 '17 at 14:43
  • per the diagram, you wired the Timer "Neutral" wire to Nest "N" and the Timer "Live In" wire th Nest "L" then Timer "Live Out" to Nest "3" and a second Timer Nuetral wire if it was there, to the "N"? The "L" for nest also jumpers to "2"? (Is this how you had it) – noybman Aug 20 '17 at 14:51
  • Neutral to N, live in to 2, live out to 3, jump between L and 2 – Antonio MG Aug 20 '17 at 14:52
  • That appears to be line voltage timer. Nest is 24v – Tyson Aug 20 '17 at 15:03
  • Sorry Tyson, what do you mean, have I connected something wrong? – Antonio MG Aug 20 '17 at 15:09
  • It seems you connected it the way the diagram suggests. Do you have a multi-meter? Also, have you re-verified the system works with the old timer back in place? Did you potentially jumper 2 to N? The photos of the wires you have to work with will be tremendously helpful – noybman Aug 20 '17 at 15:19
  • I will try again later and I'll take a picture of the nest connected. The old timer is back and working fine. – Antonio MG Aug 20 '17 at 15:24
  • 1
    Good, that helps validate the unit didn't fail for some other coincidental reason, and further proves it is a wiring issue, OR a bad nest issue. Please take photos of the BACK of the old timer with wires attached before you disconnect. Then feel free to photo the nest hooked up. A second or 10th pair of eyes can help. – noybman Aug 20 '17 at 17:24

2 Answers2

2

The guidance we are/have been providing in the comments.

The direct answer, is that you have a current carrying wire directly tied the return. (E.g., Neutral & Live In wired together). While this may not be exactly what happened, its an example.

Unfortunately, the diagram the book shows you is possibly misleading and therefore it is likely you were able to either misinterpret the wiring, or just juxtaposed a wire. It i also even possible that the Nest could be damaged or faulty, but vetting the wiring used will help ensure that is not the case. If it is, return it for a new one.

The pictures help to ensure any guidance given is sound, since there are many possible things that could actually come into play to cause an issue like this.

If you have a multi-meter it is invaluable. It is best when doing these types of connections to always ensure without any doubt each wire is what you think it is. So performing OHM tests between L & N, or End to End on a wire is a great way to have this surety.

Only then, would you turn the power on. Nearly eliminating any chance of damage to the equipment, or you.

noybman
  • 1,997
  • 12
  • 23
2

The object in the photos is a 230V "immersion-heater timer". Most traditional UK heating systems have a "programmer" instead but I guess you could have an installation that just uses the timer. I'm assuming IE practices are similar to the UK.

In that case, wire 1 on the old timer would have provided switched-live to a 230V thermostat and the 230V thermostat would switch that live power to the boiler when needed.

If you just took the wires off terminals 2&3 on the timer and attached them to 2&3 on the heat-link, the heat-link would, when calling for heat, short neutral to live and trip the breaker. But I doubt you've done that because you wouldn't then have power to the heat-link itself.

I assume that you repurposed the wires that previously carried 240V live out to the thermostat and switched 240V live back so that these now carry 12V power to the Nest (as shown by T1, T2 in their diagram)? Presumably you disconnected any redundant wire(s) at both ends and made it safe (e.g. connect to ground at both ends).

I would turn off the breaker, disconnect the wire from terminal 3 of the heat-link, isolate that wire in a connector block by itself, turn the breaker back on and then carefully use a voltage tester to check that all the wires were as expected and that terminal 3 is initially dead (near 0v) but goes live when the heat-link/Nest realise that heat is needed.

RedGrittyBrick
  • 24,033
  • 11
  • 46
  • 88