How to tell if OWB is leaking?

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New Member
Dec 15, 2021
Central NY
Hi all,

I have a '98 Central Boiler Classic OWB. I inherited it with my new house and ran it last April and May and the beginning of this heating season. The previous owner showed me how he used it (he lives next door), and it seems to do it's job as well as it can given the design.

I cleaned out the ash last weekend. It was a rainy day, and due to the siting of the shed the OWB is in, water will seep in there, but it usually is gone in a couple days. There is now persistent water around the OWB and it seems the rest of the water that seeped in is gone. I'm wondering what the procedure is for checking for leaks?

I filled it with water, actually a little too much, in October. The water guage doesn't show anything (if I'm using it right?), and I ended up filling it enough that it pushed out of the furnace, dribbling out of seams around where the roof meets the sides mostly. It has seemed to function well, and I haven't had any other troubles this season. It now is showing a little leaking from those areas, which it may have been doing all along, I just haven't noticed. But there is significant water around the OWB. Perhaps a leak somewhere else? There were a couple places with wet/clumped ash when I cleaned it out. Pics are below.

I'm also wondering about the Aquastat. It doesn't offer a readout, but it seems to do the job otherwise opening and closing the side damper. Any thoughts on examining that as well as welcome.

Water around OWB

Little Puddling


Water Leaking down from where roof meets sides/front


Broken Aquastat



Feeling the Heat
Dec 12, 2017
Not familiar with CB but you should have some sort of fill port with a water level indicator. Check to see how much it drops over time. Typically being an open system you will only loose 1 gallon every year to evaporating. Also remember to check at operating temperature as water expands and contracts. Hopfully that helps.

For reference I have a Polar Furnace G-class they have a similar water level indicator as the Portage and Main updraft boiler.


New Member
Jul 31, 2022
1st pic, upper right.
This is a different model from what I had, but that looks like their simple water level indicator.
A brass valve elbow with a clear tubing, running vertical. Open valve, if there is water in tube, there is water in boiler. Closing valve should drain the tube so it will not freeze.