I have an odd problem with my tankless Weil MacLain water heater. It seems that in the winter the water fill doesn't work right. I have had the unit checked out by the servicing company and received two different responses. The first guy told me I needed to bleed the system every week. The second told me that I needed to make sure the water level was at or above the level mark and that whoever plumbed the system didn't get the pipes correct. I think I believe the second guy more. However, over the summer, I didn't have too much trouble with it. Now that it is winter, it seems that the system doesn't fill properly. Every time I want to shower, I have to go down to the basement and fill the water tank. Why does this occur more in the winter? And, how do I fix it?
You have a leak somewhere. Constantly filling a boiler with fresh water leads to early death. But, an old one may be a prime candidate for replacement when you can swing it. It will save you money in the long term. It probably occurs more in winter because your leaks are somewhere in the heating runs to the radiators and in the summer, no water flows there. It could be the pump is leaking when it runs as well. Well, there are other things as well, but you get the idea.
An internal coil in a boiler for domestic hot water is probably one of the most inefficient ways to make hot water...you need to keep the boiler running winter/summer constantly. An indirect is MUCH more efficient, as the boiler may only need to run once a day or so after a bunch of showers. They're generally so well insulated that they will keep water hot for at least days without the boiler firing.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013