Smart T-Stat installation: Low Voltage output on Burnham MPO IQ Boiler Control

kbogden

I am a DIY'er with little experience with boilers attempting to install an ecobee 3 thermostat before the winter and am running into some difficulty. It appears the voltage output on the control system (see page 9 of wiring manual in the link below) is low with direct terminal readings on my multi-meter for Rh-W (Left-T and Right T in schematic) of 14 volts and Rh-C (C wire is Terminal 3 in schematic) of 2 volts. The output for Terminal 2 and 3 leading to the Indirect Water Heater read 24 volts. My meter readings are directly from the terminals not from the t-stat wires in the wall. According to the schematic in the link below, it is a 24 volt system, does anyone have any advice as to why the voltage output from my boiler is below 24 volts. The multi-meter readings with the indirect water heater disconnected are the same as above.



I very much appreciate any help with this issues in advance.

https://www.thermoflo.com/wp-content...e+-+MPO-IQ.pdf

Regards,

Ken

nicholas bonham-carter

My experience with the Ecobee showed me it needed a lot more juice to power up the wireless functions, than my boiler transformer was able to provide, and so I just kept my Honeywell VisioPro.—NBC

HVACNUT

The left T' will go to R on the Ecobee.
The right T will go to W on the Ecobee.
Terminal 3 will go to C on the Ecobee.

I've never used the Ecobee so if theres A/C involved, you must separate Rc,Rh by removing a jumper, program it to separate, or maybe the Ecobee recognizes there are 2 R power sources.

If you have A/C, use its transformer to power the thermostat, R and C and you'll connect TT on the board to Rh and W on the Ecobee.

Like @nicholas bonham-carter wrote, if your going to use the boilers transformer, make sure it can handle the load. At least 40va.

kbogden

Thanks for the responses. The boiler is only rated for 24 Volts so that could be the issue.

HVACNUT - I attempted the setup as you described above initially. However, with a multimeter, the Rh-C terminals (on the boiler) give me 2 volts while the Rh-W terminal gives me 14 volts. I believe both those tests should give me a reading of 24 volts, which is the voltage required for the ecobee. Any idea of why i would get these funny readings?

Unfortunately i do not have central A/C to power the ecobee.
Thanks again

GBart

They aren't talking 40volts, they mean 40va as in watts, transformers are rated in watts, usually a gas appliance may not have the power to run the units controls and a wifi t-stat, the transformer has to be 24VAC and 40VA (watts) or larger.