Honeywell screen went blank

Master Brian · 12-22-2010, 09:35 AM

I have a Honeywell Vision Pro IAQ YTH9421C1002 Verson 2 Thermostat. Last night when I got up in the middle of the night, I noticed the screen was blank and no light coming from it. A minute or so later and it was back on again. When I got up this morning, it was again out, yet the furnace was blowing. I pulled the face away from the wall mount plate to see if there were any visible batteries, but of course there were none. When I placed it back on the wall it lit back up again. Everything seemed ok....temp was were it should be, it registered the outdoor thermo, indoor humidity, etc....

Any ideas why it's doing this? I don't know if this is a sign of the screen itself going bad, the interface module, or something else.

Again, I didn't see a battery, but I'm guessing there is a battery to hold memory somewhere, could it be that and if so where is it located? Wasn't sure I should pull the face apart.

Thanks for any input.

hvactech126 · 12-22-2010, 04:09 PM

chk wiring connections... and tighten both at stat and at EIM. Sounds like display is going out. inside the stat is a watch battery but only to retain memory.

Master Brian · 12-22-2010, 07:04 PM

Well, I haven't checked this evening, but so far it's stayed on that I see since pulling it off the wall and putting it back on. I will check the connections as well. I suppose as long as it's just the display that goes out and if the unit still functions, I'll be ok. I just worry about loosing it and loosing heat at the same time. I have standard t-stat's I can replace with, but prefer not to have to re-wire one, just to wait a week on shipping for a new IAQ unit....

hvactech126 · 12-23-2010, 06:25 AM

Quote:

Originally Posted by Master Brian

Well, I haven't checked this evening, but so far it's stayed on that I see since pulling it off the wall and putting it back on. I will check the connections as well. I suppose as long as it's just the display that goes out and if the unit still functions, I'll be ok. I just worry about loosing it and loosing heat at the same time. I have standard t-stat's I can replace with, but prefer not to have to re-wire one, just to wait a week on shipping for a new IAQ unit....

that stat has a 5 year warranty

Master Brian · 12-23-2010, 02:47 PM

Quote:

Originally Posted by hvactech126

that stat has a 5 year warranty

I was wondering about warranty, that is good to know! Thanks!

Dave Carney · 12-23-2010, 03:21 PM

FWIW, when my system was installed the installer did not push the unit back onto the mount far enough before he left, and we had similar weirdness as soon as he was gone. He came back and in pretty short order determined what the deal was. Pushed it all the way on, no problems in a year and a half.

SKIP4661 · 12-23-2010, 04:14 PM

I suspect the furnace is opening the limit switch due to an overheating situation thus killing the low voltage to the furnace and stat. You may want to check your filter and make sure all registers and grills are clear and open.

**beenthere** · 12-23-2010, 09:32 PM

If your furnace is a condensing furnace, and its condensate drains to a condensate pump. See iif the safety switch of the pump is wired to break the Power to the EIM. If so, your pump is having a problem.

Master Brian · 12-25-2010, 03:38 AM

Quote:

Originally Posted by SKIP4661

I suspect the furnace is opening the limit switch due to an overheating situation thus killing the low voltage to the furnace and stat. You may want to check your filter and make sure all registers and grills are clear and open.

I'll check that. The filter is due to be replaced as the display is flashing such, I'll go ahead and replace it even though the current filter hasn't been in the full 30days yet, I had checked it a few days before it said to change and it still looked pretty good, but maybe I'm wrong. It hasn't happened since I pulled it off and pushed it back on, but certainly don't want to overheat the furnace......

All drains of the furnace & a/c lead to a sump pump.

Thanks for the replies!

Focker · 06-25-2012, 12:42 PM

I just went through this problem over the weekend. The system is 9 mo old so I didn't mess with it. The tech fixed it in 30 sec after finding a blown 3 amp automotive fuse on the circuit board inside the furnace. I felt stupid that I didn't see it but then again any chance of me NOT voiding a warranty is a good thing!

**beenthere** · 06-25-2012, 05:49 PM

But what caused the fuse to blow.

how · 06-25-2012, 10:13 PM

Just to advise of a new wrinkle to consider.
I don't know if smart meters are being installed elsewhere but some of the young twits installing them in my area have been causing 24V issues with furnaces, doorbells and appliance clocks.

Focker · 06-25-2012, 11:53 PM

Quote:

Originally Posted by beenthere

But what caused the fuse to blow.

A possible short...but the tech seems to think the 3 amp fuse is under sized from the manufacturer. He replaced it with a 5 amp. He said if it pops again he'll hunt down a possible short.

Sent from my mobile using DIY chat room app.

hvactech126 · 06-26-2012, 05:53 AM

Your tech is a moron. Many systems come with a 3A fuse. Put the correct fuse back in there before you blow your transformer.

biggles · 06-26-2012, 06:03 AM

dow you have wires on R and C for a constant 24Vs from the furnace take a Q-Tips wipe the contacts/pins with alcohol..vodka,gin,...whatever

doubt a furnace hi-limit knocks it down, condensate pump might if you have one see

if you have low voltage wires going to it