I'm sorry, what you wrote is confusing and difficult to understand. Is it a boiler or a furnace? Either one if the vent froze over it would stop working if vented correctly so, moisture in the house statement makes no sense.

Better description and pictures please.

Sorry... it is a 90% efficient Rheems gas CFA furnace. It takes moisture out of the inside air somehow during the heatng process & releases it outdoors (or into a drain in the house). Since this was installed in an older house it was easier I guess for the furnace guy to run the drain tube up through the roof & it is on the end of this tube/pipe where moisture freezes the tip shut some cold nights. The furnace still works but the moisture now escapes into the house instead of up the drain to the roof where there is ice. Since there is no moisture at all times in the drain, most heat tapes I have seen say NOT to wrap empty pipes with the tape. Hope I have explained a bit better?

This is a interesting post. A 90+ furnace might have a stack that goes thr. the roof. But drains do not go up, they go down hill. How many stacks do you have going up and out the roof, and what size are they? If you do have a drain going up thr. the roof it would have to be pumped up with a condensate pump.
Its sounds like you need to have another heating tech look at your system and check it out, Just to make sure you are not getting gas fumes in the house. paulbm

"It takes moisture out of the inside air somehow during the heatng process & releases it outdoors (or into a drain in the house)."

This makes no sense.

Heaters do not remove water from the air (inside or outside).

There are condensing furnaces that have such low temperature exhaust it does not require a high temperature metal flue, but the water is coming from the fuel being burned.

I cannot recall a 90% condensing furnace, most of them are 95%.
If moisture from flue gases is present inside the house you have a very serious problem.

Flue gases contain carbon monoxide and can kill anyone who breaths enough of it for a long enough time.

A quick search shows Rheem has no models with CFA.
Perhaps you are abbreviating "Condensing Forced Air"?

In that case no condensate drain lines should ever be run to the roof, since they must never be run where freezing conditions exist.

Sounds like he is pumping it up and expecting the roof and gutters to handle it.

If this is the case, you have a improper, damage causing and dangerous condition that must be corrected as the original installer is clueless and failed to follow proper installation procedures, or the installation manual provided with the unit.

I probably am not relating the proper way the furnace functions even though the plumber & the City Inspector tried to explain it to me- a woman! This furnace takes all the air from the outside to burn so does not require it to be enclosed in the house. The water (actually: 'moisture') comes from the ? fuel .. not sure but is a by-product of the combustion so this moisture has to be vented somewhere. In new homes it can be vented to any household drain but in my old house the easiest & cheapest way was to vent it via a small pump on the floor (yes,thank you paulbm .. what you described?) up through the roof the roof. Works fine until freezing weather & the end of the tube on the roof freezes the moisture. The #'s on the info. package: Rheem 90+ upflow RGRA-06EMAS278 F1008. 0It is an updraft central forced air to other rooms
F1008
When it is on, the furnace produces a slight noise,hum that can be heard outdoors.
Hope this helps to explain this furnace. The Gas Co.& City Inspectors checked all the work of the furnace man before green tagging it so hope it is OK.

You have a simple sealed combustion condensing furnace.
The quick and simple answer is, condensate produced during combustion can never drain or be pumped to a area that freezes.
You have a bad installation and clueless inspectors.
It must be rerouted.

What is under your house? Do you have a cement floor where your furnace is at? Is your furnace in a basement? Or do you have a craw space under the floor?. paulbm

Yes, cement floors, no basement, no crawl space unfortuntely. If heat tape would work the problem would be easy to solve but can't wrap an empty (most of the time) pipe with the tape the directions say. Hmm!

Thanks for the patience in trying to understand what I was trying to say!

A 90+ furnace does not make that much water, so what i have done many times is, depending on what kind of dirt is under your cement, Have some one put a 7" round hole through the floor and see if you have sand down there. I put a 6" plastic
pipe about 20" long down in the hole and take the dirt out.
You can put a gal. of water in the pipe and see how long it takes to soak away. Depending on the size of the furnace, it will not make more than 1 QT per hr. of water. If there is clay down there , this will not work. later paulbm

Tap the condensate line or pump discharge hose into the plumbing vent going through attic headed to roof, as a last choice.

unfortunately-again- the soil is clay one could make pottery out of! If the water drain line can run at angles, I guess it could be run along the floor to the adjacent bathroom & hook into the drain there. In these old houses it is difficult to retrofit it to new City standards; so far 90% furnaces are not yet required but since this old 56 yr. old original (& still working fine)needed to be replaced at some time anyway, the 90% seemed the way to go esp. as the old furnace was not enclosed (huge outside vent to roof near floor bringing in the fresh-& COLD!- air) & was up to code back then unless it had to be replaced, any new furnace of that type would need carpentry work to enclose it in a closet & vent to roof to current code so the 90% seemed the one to get as it was not required to be in any enclosure in the hall.

When the furnace comes on this new one can be heard: a low sound outdoors which was told is normal for this kind of furnace! Otherwise it is heating well (cycles a lot) & gas bill is lower which was the reason for getting it!

Thanks for all of your help!

If you are using a condensate pump, then the condensate line can be run almost anywhere, around corners, over and under, where-ever. If you have a path to some inside plumbing, that would be the place to put it. Under no circumstances can it be ran outside in freezing temperatures. Besides that, it is very corrosive and I don't think I would want it flowing down my roof. Demand that your installer re-route it to a proper location, then never call him again.