Hot water heat / furnace question

[flatbutt]

Hey gang, my son just bought a home with hot water base board heating. Every couple of days the low water cut off trips and he must add a bit to get the system up again. We can't find a leak anywhere nor do we hear any steam escaping when it's running.

I know nothing about these systems. So any tips greatly appreciated.

[oldE]

Any steam visible from the flue? Leak might be in the boiler.
Best
Les

[Por_sha911]

How old is the boiler? Boiler water tubes leak (and are expensive to replace).

[flatbutt]

OLD, but we're unable to find any leaks.

[billybek]

System open to atmosphere or closed/pressurized?

[cabmandone]

I'm not good on boilers but my first thought would be an air pocket somewhere.

[jpk]

Hydronic systems (boiler with circulating pump and maybe some zone vales) are supposed to be closed systems. The water temp shouldn't get hot enough to make steam - the systems are not designed for pressure, so any leaks would show as a drip or very slight trickle.
Water is leaking somewhere. Probably inside a wall somewhere that's really hard to get to.

[flatbutt]

Thanks guys, still searching.

[billybek]

This may be helpful.
link: Pressurization Of Closed Hydronic Systems

Check to see if there are any automatic air purgers (example maid o mist) on the system that may be allowing water out of the system.

Quick question, is there a boiler temperature controller that ramps the temperature up with a drop in outdoor temperature?
The reason I ask this is because I have seen this type of controller take the system temperature/pressure up when the expansion tank is full of water/no air space to allow for expansion. When the pressure goes up, the water is forced out of the system on a relief valve (over pressurization). It operates ok until the outdoor temperature goes up and the boiler supply water temperature drops. When the temperature drops so does the pressure and then you see a short of water situation.

Suggestions:
Make sure that the expansion tank has the proper air charge if it is a bladder tank.
These do go bad on occasion and they lose their air charge.
Make sure that there is an adequate air charge in a non bladder type pressure tank.
Make sure that the expansion tank is large enough to accommodate all range of pressure and temperature for the system size.
Make sure pressure relief valve is not leaking. Often these will weep or outright leak. If it is piped to drain, put a pan or a bucket under it to see if it is releasing water.
When adding water to the system, monitor pressure until the loop is back up to temperature.