Nest Thermostat E now Boiler go s into Lockout

[jeremywar]

I have an old heat-only boiler system with two zones, each with its own pump and relay switch. Not actually a zone controller valve. I have two thermostats each with TT wires (Rh & W) from relay switches. I recently replaced both thermostats with Nest Thermostat Es. As I don’t have a C wire I installed an nest power controller/adapter at each relay switches (x2) and I also added an external 24v transformer for each power controller configuration. 

Now both nest are reading and working as normal, no errors and good battery charge. However now after a few good heating cycles the boiler goes into lockout mode and stops heating.

[CoolingWizard · Accepted solution]

@jeremywar, depending on the boiler that you have, those systems are not designed to have 24 V of power enter on the T terminal. Some do some do not. If yours does not accept that it will see their stray voltage coming in on T and it will force the system to lock out until it gets checked.

the way to wire this up in such a way is to not have this problem is the transformer has to supply power on the RC and the C terminal. The RH and the W terminal are separate and you set the system up as a dual fuel system. The boiler will be hooked up to Rh and W. 

AC Cooling Wizard