Question about Heating & Cooling

1 Answer

How can I modify wiring to solve a generator related problem?

I have two systems - a FHW oil fired heating system and a central A/C system on the thermostat. Instructions say common 24vac must come in from the A/C side, not the furnace side. This works fine under normal circumstances. But, I have a portable generator and a Gnerac panel wired for 10 circuits. The A/C system is not on the Generac panel; the furnace is. When I have a power outage and hook up my generator, my furnace had power, but my thermostat does not. Honeywell has been of no help on this, other than for one person to say that in no way can you take the 24vac common to the thermostat from the furnace. I have asked about several options, but cannot get them to reply. For example, put an A/B type switch off the therostate 24vac common with the ability to switch it to feed from either the A/C or the furnace. Can you comment and do you have any practical suggestions short of ditching this thermostat, which I really like otherwise?

Posted by on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Heating & Co... Master
  • 1,655 Answers

A common is basically a ground. If you had to you could run your common to an electric outlet on the ground wire. Not recommended but I have done it and it will work. I'm a southern a/c guy with no oil furnace experience but if your furnace isn't sending 24 volts to the tstat it's not going to matter if it has a common because you will have lost your 24 volts when your a/c is off. If your furnace does send 24 volts to the tstat then I don't see why you could not get the common from the same spot, even if you run your common straight to ground. Good Luck

Posted on Mar 10, 2017


6 Suggested Answers

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017

Da Brain
  • 11 Answers

SOURCE: Wiring a Drayton Room Stat into central heating system


Posted on Oct 27, 2008

  • 24 Answers

SOURCE: Honeywell RTH 230B Thermostat Wiring

put the jumper back in RC and RH and that should do it.

Posted on Apr 15, 2009

  • 1 Answer

SOURCE: 44860 thermostat won't activate in heat mode

I had the same set and problem. I had a RC wire which is the power to the AC. But didn't have an RH wire which is the power for the heat. To fix this just use the jumper wire and insert it in with the RC wire and hook it up to the RH. Fixed my problem.

Posted on Oct 16, 2009

  • 108 Answers

SOURCE: Replaced mercury thermostat w/Honeywell CT87K - doesn't work!

You need a specific thermostat for a Wall Furnace it is a Millivolt Thermostat and not a 24v standard thermostat....usually it will work anyway however if the powerpile (generator produces millivolts from the pilot light) is weak it may not be producing enough...or the Pilot light may be dirty and lazy...won't produce enough millivolts ...or you can have bad or dirty contacts or connections....or a combination of any of the above.....a 24v Thermostat and particularly a non-mercury thermostat has too much resistance in it for a millivolt your Wall Furnace (other than the fan) runs on less than 1 volt

Posted on Oct 31, 2009

  • 43501 Answers

SOURCE: st6400c thermostat wont run the central heating independantly

This does not sound like a thermostat problem. I would be looking for a zone valve or circulator pump problem.

Posted on Nov 12, 2009

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Boiler won't ignite for hot water unless heating is on.

If this is in a RV the propane monitoring valve may require more gas flow to turn on than the water heater requires. A central heating system requires substantial gas flow so when the monitoring valve opens to fire the central heating, there is enough gas flow to also fire the water heater.

Jan 26, 2016 | Water Water Heaters

1 Answer

Pulled plug and no fire

is there a low oil shut off system?remove the front cover from the engine unplug the small wire to the coil crank it over if still no spark replace the coil

Sep 01, 2012 | Briggs & Stratton Power Products 5,550...

1 Answer

Need a fan for the extreme Power Plus 600w

What a wastage of power ?
I suggest not to fan more but to reduce heat generation.
Better check, why excess heat generated? Surely low power devices overdrived. Just modify it. Like low voltage schottky rectifier. insted of using 20A per channel, they use 3A per channel. Your PCB of SMPS has the hole to cater the proper rectifiers. Just Search the datasheet, replace the overheat component with higher capacity and you solve the problem.

Sometime, poor screwing of heatsink to transistor/devices may generate excess heat too.If you can replace the fan, you must do the other work I recomend. GOOD LUCK.

Jan 29, 2010 | Cooler Master Extreme Power 600 Watt...

2 Answers

Alpha oil fired cooker (aga type) & central heating breakdown.

you dont say but i presume you have an early model 1996-2000. these had the most horrid burners ever. its wasnt untill later when the ecoflam burners were used that problems that you describe were elimanated as a standard every day problem. better still was the much later 800 series ecoflam twin burn as fitted in the rayburn 800 series this is the aga company that closed down the alpha and now produce the same cooker with better burners. who can suply used and new burners for you

Dec 25, 2009 | Kitchen Ranges

1 Answer

High running costs for gas fired Rayburn central heating

these are now a redundant range parts are no longer available and a good thing too as they cost the earth to run. gas ones cost more to run than oil. try "top of the range ltd" for a solution

Dec 20, 2009 | Kitchen Ranges

4 Answers

Brivis central heating fan will not switch off runs continuous

brivis wombat 2P 20 ducted heater, gas fires up but fan not starting
Any suggestions...???

May 12, 2009 | Heating & Cooling

1 Answer

Thermostat not firing central heating

the stat works using a bi metalic strip so that click you here is making a contact and telling the boiler to call for heating so if you getting no click you need a new room stat. Replace with same model and note the wiring most stats only use 2/3 wires depending on system

Dec 08, 2008 | Dayton Electric Heater

1 Answer

My Central heating wont come on. There doesnt seem to be any lights on the boiler/burner. Why could this be. First time I've tried to turn it on this was fine back in february. Thanks!

Is the switch off?

Check the fuse panel/breaker box.

Is the thermostat switch set to heat?

Is system oil heat? If so check the following...

Some systems that use oil have an emergency switch (sometimes with a red plate) located away from the unit usually the basement staircase.

The oil systems also have a heat element above the burner on ceiling that "trips" if there is excessive heat. This shuts everything down so as not to feed a possible fire with oil.

Check the gun (burner itself) and try and locate a little red reset switch located near the back side of gun. Try pushing it in to see if its tripped.

If these quick checks don't help then it would be wise to call a technician to check your system for issues. Heating systems are too critical to "play" with and problems are best left to the pros for safety's sake. Good luck, I hope this helps.

Sep 16, 2008 | Heating & Cooling

1 Answer

My oil fired central heating system has stopped heating up stairs.The rads and pipes have been flushed out,when the system was refilled the upstairs rads heated ok untill the system was switched off for...

Since you have done a good job bleeding the system, I will suggest that the impeller on the pump is bad. Many times these will simply deteriorate in the volute causing the symptoms that you describe.

This looks like it is in the wrong forum. Try reposting this in the heating section of the FixYa web site to get more responses.

Jul 03, 2008 | Heating & Cooling

Not finding what you are looking for?
Heating & Cooling Logo

Related Topics:

1,026 people viewed this question

Ask a Question

Usually answered in minutes!

Top Heating & Cooling Experts

Paul Carew

Level 3 Expert

3150 Answers

Dan Webster
Dan Webster

Level 3 Expert

8220 Answers

Tim Whalen

Level 3 Expert

3074 Answers

Are you a Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides