I am installing a Honeywell RTH 7400 D. The old thermostat did not have lables on the wires. There is a Red White and Blue Wire. I believe the Red will go the Rh and the White to W but I do not know where to connect the Blue.

What was the brand and model of the old thermostat. What numbers/color designators were on the old thermostat.

Check the air handler/furnace. Where is the blue wire attached to on there?

The old thermostat was a Honeywell T87 F1800. It did not have any lables where the original wires were connected.

On the old thermostat there was a sub base where the wires were actually located. What is the old sub base part number?

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Originally Posted by hvac1000

On the old thermostat there was a sub base where the wires were actually located. What is the old sub base part number?

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Thewre was a brown plastic disk that was the base but there are no numbers on it. The actual thermostat is labeled T87F1800 2 7845. The only other numbers is a 3A on the underside of the unit.

Look at figure 6 in the below instructions

http://customer.honeywell.com/techli...0s/60-1175.pdf


You never mentioned exactly what you are trying to control with the thermostat. The wiring diagram (6) is for Honeywell series 20 or the old style White rodgers zone valves. I am actually at a loss as to what you are really doing since you never mention it in your posts

The thermostat is for heating only. It controls a Burnham V-34 oil burner.

Sorry if it is for heat only usually the R (RED) and W (WHITE) are the only wires used unless it has additional controls.

No search on Burnham website disclosed any info on your V-34 unit.