520 Domestic Hot Water Problems and Other Issues

Hello All! I just registered here so I apologize if my following post has been answered before or is something that is painfully obvious.

First off let me be up front and say that I do not know alot about furnaces or coal stokers in general so forgive me if I have some bad terminology or don't know what you might be referring too. On to the issue.

I have a DF 520 in my house that we use to heat the house with hot water base boards and heat the domestic hot water with. It seems that we have had no stop issues with this furnace since it was installed. Admittedly some issues were probably not related to the furnace but some seem to be. The issue currently is the hot water coming from the domestic coils seems to be totally sporadic. The temp on the furnace will be be around 180 and water coming from the tap will be luke warm. Other times if allowed to run a bit the water will become scalding hot but then return to luke warm. The water comes out of the coils and to a hot water tank that is currently turned off. Another thing that I noted is the pipe coming out of the domestic coil is not very hot. I would think that this should be almost untouchable.

To provide alittle more information. There hasn't been a fire burning in the furnace for roughly 3 weeks. I had the fire shutdown because I had to replace the burner plates in the pot due to them being cracked and warped (this is also another on-going issue...). I realize that having it off for that long of a time was probably not the best situation. However water was still constantly running through the domestic coils to the hot water tank that was at that time turned on to heat the hot water. Also the water for the base board heat was also drained out of the furnace for most of that time as I replaced the circulating pump.

Any help or insight would be appreciated!

/J

Welcome to the board

How old is this boiler? How old is the hot water heater tank? Is it electric or gas?

McGiever wrote:Welcome to the board

How old is this boiler? How old is the hot water heater tank? Is it electric or gas?

The hot water tank is electric and was installed in 2009. The boiler I believe is around 8 or 9 years old. Off hand I can't recall the exact date we installed it. I just noticed after the boiler gets done doing a burn I can sometimes here bubbling noises coming from within it somewhere. I assume that's not a very good sign. I can't see and water leakage or drainage though.

With the water coming out of a boiler at 180, the pipe should be scalding hot.

The water going to the hot water tank ideally needs a pump to circulate the water to the tank and get it hot top to bottom. There is just not enough gravity circulation through half inch pipes. The only time it circulates adequately now is when you open a tap and then into a tank only partially warmed.

Unless you really need a lot of hot water why not just pipe direct to the tankless coil in the boiler, which hopefully is rated at 5 gallons. The bad part there is that a coal fire will not respond nearly as fast as an oil fire.

First thing, need to have hot water come out of the coil.
If not...need to find out why not.
Is there a thermostatic mixing valve after the coil somewhere?

I don't think there is any value after the coil. Here is a rudimentary diagram of how it is plumbed.

Public water --> indoor water pump (we have poor water pressure coming in) --Split to boiler--> boiler domestic coil --> electric hot water tank --> the rest of the house

The line from the coil to the hot water tank is a straight shot with no extra valves, other than a shut off valve right after the coil and a shut off value before the hot water tank. I can bypass the hot water tank but I really don't think the hot water heater tank is the problem here as the water coming from the coil seems to be cold or barely warm most of the time.

Is there a way for me to somehow test the coil? or is pulling it out really my only option?

First answer McGiever's question and if there is no sort of mixing valve between the cold in and hot out and the hot out pipe (not faucet water) is only warm with a hot boiler then the coil becomes suspect. Could be loaded with rust mud in the fins. How did it work when first installed?

There is no thermostatic mixing valve that I can find. I did not do the plumbing so that's why I said I wasn't sure. The hot pipe out of the coil is not hot only warm. You can easily put your hand on it and not have to take it off. Boiler temp is still 180.

It was working great before I had to shut the fire down. Water was always hot. If taking a long shower or washing multiple loads of clothes the boiler temp would eventually fall below the minimum setting and begin firing again. The water temp from the faucets would remain hot. I always thought that's how the system should work?

So the poor hot water started after your shutdown? I don't mean to insult your plumbing abilities, but are you positive the boiler is full of water and free of air?

Rob R. wrote:So the poor hot water started after your shutdown? I don't mean to insult your plumbing abilities, but are you positive the boiler is full of water and free of air?

Exactly, after refilling the system it takes some procedures to get all the trapped air vented out of the boiler system. Air pocket remaining trapped will cause reduced hot water output as you are experiencing. .

OK, so I am sure that I have an air pocket in the hot water radiator system, because like said I replaced the circulating pump which would open that to getting air in it. Since these were separate systems in a sense I was thinking that the domestic coil would still operate correctly on its own. Forgive my ignorance if this would have seemed obvious, as I said I'm obviously no expert.

Is there a "proper" way to effectively bleed the boiler system? or do I continue to try and use the air bleeders that are connected along the radiator system?

Thanks for everyone's help so far, I really appreciate it.

Im guessing when you shut down you somehow isolated the expansion from the boiler and when it cooled it sucked air in an automatic purge valve on top of the boi;er...maybe? In any event the top of your boiler is likely full of air and the coil is in the top of the tank , in a hot air bath.

Well those of you who suspected an air pocket in the boiler were correct. Everything seems to be working correctly now!

Thanks everyone that posted! I'm sure I will have more questions in the future.

Good, glad you were able to get it back going again.

Good call Robb!