Weil-McLain Water Heater Leaking
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The Short Answer: On a Weil-McLain Aqua Plus indirect water heater, a leak from the side inspection plate is often the thermostat drywell corroding after the magnesium anode wore away. Weil-McLain’s service bulletin says that leak is fixed by replacing the inspection plate, not the whole water heater. Other leak sources include the relief valve, pipe connections, and the boiler-coil connections. Only a leak from the tank body itself means replacement.
Find where the water is coming from
Dry each area with paper towels, wait a few minutes, and see which one gets wet again.
| Where it’s wet | What it usually is | Typical outcome |
|---|---|---|
| Side inspection plate, crusty deposits around the thermostat well | Corroded thermostat drywell (part of the inspection plate) | Replace inspection plate and anode; check thermostat |
| Relief valve or its discharge pipe | Relief valve opening on high pressure or temperature | Check house pressure and expansion tank; possibly a new valve |
| Hot or cold domestic water connections | Fitting leak | Repair the fitting |
| The two boiler pipes (coil supply and return) | Boiler-side joint or valve leak | Heating technician repairs the joint |
| Insulation or jacket wet with all fittings dry | Tank leak | Replace the water heater |
| Floor wet, tank dry | Boiler relief valve, zone valve, condensate line, or other equipment | Keep looking |
Water from the boiler loop often looks discolored or has an odor from treatment chemicals. Domestic water is clear.
The inspection-plate drywell leak
Weil-McLain fits every Aqua Plus with a magnesium anode to protect the weld joints of its stainless steel tank. Its service bulletin SB-1401 (opens in a new tab) explains that if the anode is completely used up and not replaced, corrosion can begin on the thermostat drywell, which is part of the inspection plate, and lead to a leak. For a drywell leak, the bulletin’s guidance is to:
- Replace the inspection plate (the drywell is part of it); the water heater does not need replacing.
- Check the anode and replace it if needed. With a drywell leak, the anode is most likely fully depleted.
- Check the thermostat’s sensing bulb and replace the thermostat if the leak damaged it.
The bulletin also states that anode, drywell, and thermostat replacement is not covered under warranty, and that the anode must be inspected at least annually.
What you can do now
- If water is spreading, close the cold-water supply valve to the Aqua Plus.
- Turn off the boiler’s hot-water call, or the boiler, using its normal controls, so it stops heating the tank while it waits for service.
- Photograph the leak area, the rating plate, and any valves for the technician.
Do not remove the inspection plate, the anode, or boiler piping yourself. The tank is under pressure, the plate holds the thermostat, and the boiler loop needs to be refilled and purged correctly.
What the technician will check
They will confirm the leak source, check the anode, and for a drywell leak, replace the inspection plate and anode and test the thermostat. For relief-valve discharge, they check house water pressure, the expansion tank, and the tank temperature (a high boiler temperature can push the tank too hot). For a coil leak, they check whether boiler water is getting into the domestic water, which shows up as boiler pressure dropping while the domestic side gains pressure. A leaking coil or tank shell means replacing the water heater.
For no-hot-water problems rather than leaks, see Weil-McLain indirect water heater problems. For general leak tracing, see leaking from the bottom.
Frequently Asked Questions
Q: Is my Aqua Plus ruined if it leaks from the side? A: Not if the leak is at the inspection plate’s thermostat drywell. Weil-McLain says that is repaired by replacing the plate. A leak from the tank body with every fitting dry is a different matter.
Q: How can I prevent this leak? A: Have the anode inspected at least once a year and replaced when it is worn, as Weil-McLain’s bulletin directs. If anodes wear out quickly, have the water tested.
Q: Will warranty cover the inspection plate? A: According to the bulletin, no. Anode, drywell and thermostat replacement after this type of corrosion is not covered.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Weil-McLain service bulletin SB-1401: Aqua Plus water heater maintenance, anode inspection (opens in a new tab)All Weil-McLain Aqua Plus indirect-fired water heaters.
- A. O. Smith technical bulletin 51: puddles around a heater (opens in a new tab)Common water-leak sources and the distinction between fittings and a failed tank.
- A. O. Smith technical bulletin 45: thermal expansion (opens in a new tab)Background on pressure rise in a closed water system. Pressure testing and repairs are professional work.
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