We have a 90% efficient furnace in the office. The type that uses pvc pipe for exhaust since the furnace extracts almost all the heat from the furnace before exiting. The furnace kept going off line with a vent switch indicator light. 3 blinks. we checked and changed everything. (vacuum switch, circuit board and suction hose) Last check was on exhaust motor for any leaks. Had helper go outside and with blower fan on see if air was coming out exhaust.

VERY little. Removed cover and found hugh wasp nest blocking exhaust 70%. Removed it and furnace hasn't skipped a beat since.

WHODA THUNK?

I hear ya, myob.

Amazing what a little Condensation (in a line)

will do, also.

There are end caps that can go on the intake and exhaust. Kids putting rocks in the pipes is fairly common. I've been moving the furnace pipes to the front of the house whenever they might need moving. Then I can see as I drive by if they've been broken off . Kids climb on them, possibly to get in windows. I just landscape around with prickly bushes, so the kids leave them alone.

The vent pipe on a high efficiency furnace can also clog with ice and snow.....especially if its angled the wrong way and subject to winds.

Vee, I definitely wouldn't move the pipes just to keep an eye on them. One set I moved because the pipes ended directly in front of the side steps, exhaust blowing directly in anyone's face who was going into the house, and it dribbled condensation on the sidewalk. Yeah, directly in front of bottoms step is where I want an ice puddle. Nope. The other one was a transition to high efficiency, and changing out poorly designed duct system, so, since I got to choose where the exhaust went, I chose the front of the house. Surprised the HVAC guy a bit, but, I painted it to match the house, and there are shrubs around it. Hardly noticeable.

I wish I never did it.. (5 Navien systems)

I still have one that the plumbers can't seem to figure out.

The domestic hot water side, the hot water will run for 5-10 minutes randomly the system would stop feeding hot water as of the faucet is off. The flow sensor has been replaced twice so definitely not that problem.. contacted the manufacture, not much help either.

The system would do the same after it went back on standby mode.

Good tip - but ours came with a screen already in the exhaust port, so we're good.

As for snow, my hubby found that one of those galvanized window well semi-circles, placed over the vent pipe exit to form an arch, works great. (Full disclosure - our vent is not the type that looks like a candy cane, just comes straight out above the sill plate.) When there is a lot of snow, we still have to check for drifts, but we rarely have to clear it.