Hi, I had wired a Thermostat to a 2-wire heater (Baxi ECO 240Fi), following the instructions in the installations and user guide of Honeywell Thermostat RTH230B, Rh and W terminals. My problem is that the heater is always ON, no matter the temperature is over or under Set-Point.

What am I doing Wrong?

I'll be very thankful of any help...

Hi, I had wired a Thermostat to a 2-wire heater (Baxi ECO 240Fi), following the instructions in the installations and user guide of Honeywell Thermostat RTH230B, Rh and W terminals. My problem is that the heater is always ON, no matter the temperature is over or under Set-Point.

What am I doing Wrong?.

I'll be very thankful of any help...



The "standard" wiring for a thermostat has the red wire supplying power to the thermostat from the 24 volt transformer located in the furnace or oil burner primary control.

The white wire is energized when the thermostat "calls for heat" (and the system selector at the thermostat is in the HEAT position) supplying power back to the furnace to initiate the burner action.

The green wire is energized when the thermostat FAN AUTO / ON switch is turned to the ON position.

The yellow wire energizes the cooling function when the thermostat "calls for cooling" and the system selector at the thermostat is in the COOL position.

Some thermostats will have additional terminals for multi-stage heating, cooling and heat pump connections.

Some thermostats will also have a C terminal which is used for programming functions or internal lighting. The C terminal is connected to the "other" side (other than red) of the 24 volt transformer.

Some thermostats may have an RH and RC terminal instead of a single R terminal. Usually there is a factory-installed jumper wire between these terminals that is removed if the cooling unit has its own 24 volt transformer.


This may sound simple but do you have the FAN switch on the thermostat in the AUTO position? Do you have a manual fan on switch at the furnace?


I am not sure if there is a different wiring for this specific unit

Hi, more information, I have only two wire coming from the boiler (Baxi ECO 240Fi), both white. It hasn't a fan, no A/C compressor, only a boiler with a circuit of radiators distributed in all my house. The only function of the thermostat is to open or to unite both white wires through the Rh & W terminals. I tested those terminals with an ohmmeter reading 80 ohms when the relay is open and close to zero ohms when the relay is closed. However the heating never stop.

Hi, more information, I have only two wire coming from the boiler (Baxi ECO 240Fi), both white. It hasn't a fan, no A/C compressor, only a boiler with a circuit of radiators distributed in all my house. The only function of the thermostat is to open or to unite both white wires through the Rh & W terminals. I tested those terminals with an ohmmeter reading 80 ohms when the relay is open and close to zero ohms when the relay is closed. However the heating never stop.


I would try a different t-stat.

Seems this one may not be functioning properly, or may not be compatible with this system

I think so, thanks a lot for your help.:(...

When you take the wires off the thermostat does the heat go off. If not the problem is not the thermostat but most likely a place it the wires where they are touching or there is a relay stuck>

Yes, when I take the wire off the heat stop...