A Crazy Contraption I Rigged up. Need Help

leowis1 · Post by **leowis1** » Fri. Sep. 05, 2008 8:26 pm

Hi All,

A few years ago I installed an efm boiler along side my natural gas boiler. I have a dual fuel system. In the first year I manually switched the thermostat wires (2 of them) from gas to coal in late November and back again to gas in April (when the coal ran out). The 2nd year I installed a 4 gang junction box with light switches. I did this around January. I had two switches controlling the coal boiler and two switches for the gas. I thought I was being pretty clever. The coal boiler worked great. THEN in April I switched off the coal and turned on the gas. When the t-stat called for heat, the natural gas boiler turned on. But after the t-stat turned off, the bioler kept running! It wouldn't turn off!? So I undid the light switches and just tied the wires together. I t-stat/boiler worked fine.

Why did the light switch method work for the coal boiler and not the natural gas boiler? Do I have a bad light switch? Thank you.

LEo

CoalHeat · Post by **CoalHeat** » Fri. Sep. 05, 2008 8:28 pm

Would need to see photos and a diagram of how you did the wiring. There's got to be a mistake somewhere!

You can test the switches with an ohm meter or test light.

Freddy · Post by **Freddy** » Fri. Sep. 05, 2008 8:29 pm

If you removed a switch and wired those wires together and it worked as if the switch were 'on', you must have a bad switch. (or a three way switch and wires to wrong terminals).

CoalHeat · Post by **CoalHeat** » Fri. Sep. 05, 2008 8:30 pm

Never Ass-U-Me, Freddy!!

BIG BEAM · Post by **BIG BEAM** » Sat. Sep. 06, 2008 6:22 am

I have a new saying"just because it's new doesn't mean it's good"
DON

Steve.N · Post by **Steve.N** » Sat. Sep. 06, 2008 9:10 am

My guess would be that the gas furnace thermostat circuit is a microvolt control circuit with the control voltage generated by the thermocouple. Some switches will not work correctly at microvolt ranges, to much internal leakage. I believe that you can buy special switches to do this.

e.alleg · Post by **e.alleg** » Fri. Sep. 12, 2008 10:44 pm

I think the problem is light switches will leak some voltage across the terminals. It won't leak 120v but it might leak 5v.

LsFarm · Post by **LsFarm** » Sat. Sep. 13, 2008 12:48 am

If the light switches are the type with a lighted handle, they have the internal 'leak' or slight short through the light bulb in the switch handle.. this may be enough to trigger the digital circuits.

Greg L
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