Power stealers & circuit boards?

John Williams, Jr.

Drew the picture up real quick on autocad but was unsuccessful with posting it. Will try to scan it and post it for you later.

Glenn, you are correct with the RIB relays, they will make on 10v. AC or DC so they can be tricky. Thats why we use the IDEC's or the Square D relays with bases. Plus we are doing complete buildings. On the rare occasion that we have had to install these residential stats we found the relay to be the best solution to the problem. From a residential perspective it would seem to be the easiest way to solve this problem and make you the technician look real good. Maybe even sell a few more of those stats.

As for the relay being one more component that can go wrong? No more a problem then all the other components that have been added to residential heaters over the years. Come over to the industial side of this trade for a day and see how many controls we have on our boilers and air handlers. All those safety controls are old technology.

John

John G. Merritt

Power stealers & circuit boards?

Fellas:

Anybody hear of power stealing thermostats messing up Furnace Circuit boards? Timmie said he hadn't but I wonder if it can happen. Is it possible? I'm not sure at all.
One of my co-workers asked me that today!
I have no answer for him. (or me)

John

John Williams, Jr.

Yea John...on many occasions

it has happened with the newer Honeywell stats. We have had problems with the stats going bad and even some furnace/boiler control boards going bad. We found that by installing a relay to control the heating control for the furnace or boiler we have successfully eliminated the problem. We now install the relay with every new stat we install just to be on the safe side.

Now, how and where do we install that relay? we take the "W" terminal wire from the stat and land it on the coil of our newly installed relay, then connect the other side of the relay to common of the 24 vac loop. Then we install a wire from the "R" terminal (on the furnace or the direct 24 vac terminal on a control board) to the common contact of the relay and the other contact of the relay to the "W" terminal on the furnace or boiler.

It's been almost a year since we realized this occurance with the newer "power stealing" thermostats and we have not had any problems since we made this correction.

John Williams, Jr.
Carrier Corp.

Don in IA

Relay drawing?

Hey John,

Having trouble "seeing" what you are saying. Can you post a diagram?

Is this an official Carrier fix for all power stealing stats or just Honeywell?

Thanks for the info!!

Don in IA

John Williams, Jr.

Don...

No, its not an "official" fix to the problem, but it is very successful. On the controls side of Carrier we are doing it with any other make or model of unit because even our own stats have the same problem like those Honeywell stats.

Try to invision it and in the mean time I will try to get a drawing together for you. Here goes- at the furnace or boiler we install a simple relay (either an IDEC type (some call it a "ice cube relay") or even a RIB relay) but the relay must be a 24 vac coiled relay with its base. You would wire the heater the same as always but now you will be terminating the wire coming back from the thermostats "W" terminal to the coil terminal of your newly installed relay. Terminate the other side of the relay coil to the common side of your 24vac power supply.
Now you still need the "W" terminal on the heater to have a wire on it, so you will install a wire from the "R" terminal of the furnace or boiler to the contact of the relay. Then connect the other side of the contact to the "W" terminal on the boiler or funace.

Note, and maybe this will help you understand: The newer heaters, both air and water, are having some of their flame and air flow safties installed after the "W" terminal but before the gas valve or the other means of fuel enable. In the old days (you know last year) all of those safties use to be installed before the "R" terminal so that if any failed you would loose complete power. Well some of those switches are not always closed during normal operation, especially the air flow switches and this inturn is causing thermostats to go bad or even some control boards.

How are the control boards or thermostats going bad?
These "power stealing" thermostats actually use the "W" terminal to "drain" their power as they consume it. Want proof? Take any new stat (atleast Honeywell) and (while it is running) remove the "W" terminal wire, but do not loose connection to the burner or furnace. Your heater will stay running (of course) but your stat will go blank. Do this a number of times and eventually damage will occur either on the stats board "W" terminal (or on Honeywell, the relay in the stat) or even the furnace or boilers control panel.

Latly:
Why does this fix work?
Because the coil of the relay we installed will "ALWAYS" be connected to the common 24vac side of the power supply, which will always give the newly installed thermostat a place to "drain" its power unused.

John Williams, Jr.
Carrier Corp.

Glenn Harrison

This has been a problem for over ten years

I've been doing service for 12 years and this has been a problem since power stealing stats and integrated control boards came out. I can remember when I first got into service and having to deal with random ignition lockouts, improper timer operations, and genreal oddball erratic operation of just about any electronics using power stealing t-stats. The best thing to do is use battery operated t-stats such as honeywell T8602 series or 24 volt operated t-stats using a seperate common wire such as T8601 series. The relay does work but it is also one more thing to go wrong in the equipment.

Glenn Harrison Residential Service Tech

Althoff Industries Inc. Mechanical and Electrical Contractors

Crystal Lake, Illinois

Glenn_3

One note though, I've had trouble with Honeywells T8400B1018 operating the RIB relays. They turn on but when therm turns off the RIB relay stays on. Apparently the "trickle" charge is enough to hold the coil in. Putting their supplied resistor across the coil seems to fix it.

Glenn

John Williams, Jr.

Hope this works

well, here goes....hope this sheds some light on the subject.

And you are correct with the RIB relay that is why we prefer to use the IDEC or Square D relays instead. Yes it is one more thing that can go wrong, but enter the world of the industrial trade and you will soon learn that every heater ever made had many controls and so many different types of safety components.

Unknown

> Drew the picture up real quick on autocad but was

> unsuccessful with posting it. Will try to scan it

> and post it for you later.

>

> Glenn, you are

> correct with the RIB relays, they will make on

> 10v. AC or DC so they can be tricky. Thats why we

> use the IDEC's or the Square D relays with bases.

> Plus we are doing complete buildings. On the rare

> occasion that we have had to install these

> residential stats we found the relay to be the

> best solution to the problem. From a residential

> perspective it would seem to be the easiest way

> to solve this problem and make you the technician

> look real good. Maybe even sell a few more of

> those stats.

>

> As for the relay being one more

> component that can go wrong? No more a problem

> then all the other components that have been

> added to residential heaters over the years. Come

> over to the industial side of this trade for a

> day and see how many controls we have on our

> boilers and air handlers. All those safety

> controls are old technology.

>

> John

Unknown

Some furnaces

come with the isolating relay in the blower compartment. Its purpose is typically for twinning, but it can be used on a single furnace application to isolate the thermostat. I have a series of diagrams and instructions on wiring in one of my manuals that cover this problem.

I have found that when I was working with Honeywell as one of their Source Instructors that questions on this subject came up often. The testing that Honeywell had done showed no damage to the boards but definitely erratic operation was typical.

You definitely have to be careful with Integrated Furnace and Boiler Boards. Another problem is wiring some Zone Valves to electronic boards can present problems. In most of these cases an isolating relay would solve the problem.

Going way back with Powerpile systems some thermostats were not compatible with those systems.