Here we discuss How to Diagnose & Evaluate Leaks in or on Heating Boilers with focus on residential heating boilers, including loss of heat, heating boiler noises, leaks, odours, or smoke, and high heating costs. This website answers most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.
The photograph shows severe rust at the tankless coil on a steel heating boiler - this boiler may be beyond repair even though the rest of the unit looks pretty good.
When a tankless coil-mounting surface on the boiler itself is severely rusted it may be impossible to get an adequate seal when bolting on a new hot water coil, making it necessary to replace the entire heating boiler. It is important to recognize and accurately report the significance of rust like this on any heating boiler. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
When observing evidence of leaks on a heating boiler, keep these points in mind:
Even serious leaks may never show up as "wet" spots: A boiler may be leaking but you may see no actual water: during the heating season the boiler may always be hot, causing small leaks on the boiler or on heating piping to simply evaporate. But such leaks will usually be visually very evident: look for a build-up of corrosion, green or white or other colored mineral salts, or look for rust or water stains on the equipment.
Internal heating boiler leaks: Some critical boiler leaks may be internal and not visible by simple inspection, such as a leak inside the boiler heat exchanger which may pass water into the combustion chamber. A service technician or a skilled home inspector should be able to spot evidence of these leaks.
Surface rust, light, superficial rusting, is generally repairable. Clean the area and fix the leak when the boiler is next serviced and monitor for any future leaks.
Exfoliation, or thick flaking rust on any boiler but particularly on a steel heating boiler is very serious, possibly not repairable, and risks loss of the boiler as well as sudden loss of heat in the building.
Leaks related to temperature or pressure: Some leaks occur only at peak operating temperature--eg at relief valve. On some heating boilers such as some cast-iron units, leaks may occur between boiler sections when the system is cold - on these models some technicians prefer to keep a little heat in the boiler year-round to avoid this problem. Leaks between boiler sections may be repairable but if left unattended can destroy the equipment.
Where to Watch for Heating System Leaks
Tankless Coil mounting plate - see rust stains below and around plate
Pipe fittings at face of coil plate - mineral salts
Leaks around bolt openings - suspect hidden damage
Leaks between sections of a cast iron boiler
Leaks at the circulating pump mounting flanges
Leaks at the boiler temperature/pressure relief valve. This leak may be very dangerous as corrosion from water passing through the valve may prevent its safe operation in an emergency. Prompt expert inspection and repair are needed. Watch for leaks below the valve's mouth or discharge pipe (a pipe should extend from the relief valve to a few inches from the floor) or watch for corrosion at the tip of the discharge pipe. Gently feel inside the tip of this pipe to see if it's wet. DO NOT TRY TO TEST or open or operate the relief valve itself.
Leaks at air bleeder valves - at the boiler or remote where such bleeders are placed on heating piping or baseboards or radiators
Leaks at radiator control valves
Leaks at poorly-soldered copper pipe fittings on finned copper baseboard heating systems
Leaks due to frozen and burst piping or in extreme cases, frozen and burst heating boilers themselves
