Good point on the relay—hadn't thought of that angle yet. I've had thermostat issues pop up a couple times, and honestly, it's usually something simple like loose wiring or a dirty sensor. Before you go calling in a pro, maybe try these quick checks first:
- Pop off the thermostat cover and make sure all wires are snugly connected. Sometimes they loosen up over time, especially if you've been messing around with it recently.
- Check the batteries if yours uses them. I know it sounds obvious, but you'd be surprised how many times that's the culprit.
- Give the thermostat sensor a gentle clean—dust buildup can cause weird readings and erratic behavior.
- If you're comfortable with basic electrical stuff, take a peek at the furnace control board and relay contacts. Look for signs of corrosion or sticking.
Had a similar issue last winter—turned out to be just dust on the sensor causing random temp swings at night. Quick wipe-down and problem solved.
But yeah, if none of that helps, it might be worth getting someone in to check deeper into the furnace itself. Could be something more involved like a failing relay or control board issue.
Speaking of relays though...anyone ever replaced one themselves? Wondering how tricky that actually is for someone who's handy but not exactly an HVAC pro.
I've never replaced a relay myself, but I've watched a buddy do it once. Didn't seem overly complicated, just a bit fiddly if you're not used to working with small electrical components. He mentioned the trickiest part was making sure he got the exact replacement part—apparently, some relays look identical but have slightly different specs, and mixing those up can cause headaches.
One thing that came to mind reading your post though...have you checked if your thermostat wires run near any plumbing or pipes? I've seen cases where condensation or tiny leaks cause corrosion on wiring connections, which leads to weird intermittent issues. Might be worth a quick look while you're poking around anyway. Has anyone else run into moisture-related thermostat problems? Seems like it could be an overlooked cause sometimes...
- Good call on checking for moisture issues—hadn't even thought about that angle. I've had weird thermostat glitches before, and it turned out to be exactly that: condensation dripping onto the wiring from a nearby pipe.
- Replacing a relay isn't too bad, honestly. You're right about the specs though; I learned the hard way once by grabbing a relay that looked identical but had slightly different voltage ratings. Ended up chasing my tail for hours before realizing the mistake.
- If you're comfortable poking around, I'd say give it a shot. Just snap a quick pic of the relay and wiring before you start pulling things apart—saved me more than once when I forgot how things went back together.
- And yeah, moisture can definitely cause intermittent issues. Had a friend whose thermostat acted possessed every time it rained...turned out water was seeping in through an exterior wall and corroding connections. Worth checking out while you're in there anyway.
"Just snap a quick pic of the relay and wiring before you start pulling things apart—saved me more than once..."
Definitely second this. I've wasted too many afternoons trying to piece things back from memory alone. Moisture's a sneaky culprit, but don't rule out simple aging components either. Had a thermostat once that seemed haunted—turned out it was just old wiring insulation cracking. DIY is doable if you're careful, but calling a pro isn't admitting defeat...sometimes it's just smart.
Good tip about the photos, wish I'd thought of that before I tackled mine last winter. Ended up with a mystery wire leftover—still bugs me. Anyone ever had luck labeling wires beforehand, or is that overkill?
