Hydronic System Troubles

[Brady1]

I have been dealing with a new hydronic heating system lately, and the compression tank gets almost full of water after just a couple weeks. The system itself is said to have a leak, as it has to have water regularly added, every week or so, to keep the boiler pressure at 12 psi or more. Would the two problems be related? I don't know how the compression tank would become waterlogged so quickly from a leak somewhere else in the system? The compression tank has a sight glass so it's fairly easy to keep track of where the water level is, it also seems to fill about halfway when draining and refilling it, is this normal?

 

[Jadnashua]

Most modern boiler systems use a bladder type expansion tank verses one with air that can be absorbed by the water and then rust any iron components. A closed system with an expansion tank, if there are no leaks, fairly quickly becomes inert, and there is no further rusting of anything unless you have a leak and fresh water is introduced.

You really need to find and stop the leak. Assuming I understand what you mean by the compression tank, I'd get rid of that and install a properly sized expansion tank. If it's a bladder type expansion tank, it sounds like it's shot if it fills with water in short order. Once it gets full, expansion of the heated water may cause the overpressure valve to open, and lead to low pressure when things cool off (unless an autofill valve is opened to keep the pressure up).

Are any of the heat runs embedded in concrete (radiant heating)? Leaks there can be harder to find. Otherwise, spotting a leak just takes a careful inspection. Most of the time, people use potable water to fill the system, and that will have some minerals in it which will leave a deposit where it is leaking, if you don't also see some corrosion and/or rust stains.

 

[Sponsor]

 

[Dana]

If the expansion tank becomes so full of water that the system pressure goes too high at the end of a burn, some water will be lost at the pressure relief valve.

If there is an AIR leak in the expansion tank it can be come waterlogged, and as it's losing it's air charge the system pressure will drop when the system is relatively cool but go higher higher at the end of a burn than it would if the tank were still properly charged.

Bladderless closed type expansion tanks are really old school (can you even get them anymore?) which makes me wonder how much of the system is really new in this "..new hydronic heating system..."???

 

[Brady1]

The system is not new, but new to me, its from the 90s. As for runs under concrete, there is some and I was told that was where the leak was, but maybe I should look over all the pipes that are above ground myself? It is potable water that is added fairly regularly, what kind of damage could that do to the system over time? Pressure on the boiler gauge doesn't seem to change much from when it's relatively cold to hot, and it also has an outside temp adjustment for the temperature of the boiler. What would be the benefit of the newer bladder type expansion tanks?

 

[Dana]

Potable water is corrosive. Iron pipes, valves pumps int the system will become corroded over time, flakes of rust can jamb things up too, if not filtered. Any buried pluming should abandoned, by passed with plumbing inside of conditioned space, if you can.

 

[Plumber69]

The system is not new, but new to me, its from the 90s. As for runs under concrete, there is some and I was told that was where the leak was, but maybe I should look over all the pipes that are above ground myself? It is potable water that is added fairly regularly, what kind of damage could that do to the system over time? Pressure on the boiler gauge doesn't seem to change much from when it's relatively cold to hot, and it also has an outside temp adjustment for the temperature of the boiler. What would be the benefit of the newer bladder type expansion tanks?

you have a leak in your expansion tank. You can soap test the sight glass.

 

[Plumber69]

Bladder is less maintenence. Nothing beats visual. But always convert to bladder