Weil-McLain Indirect Water Heater Problems
The Short Answer: A Weil-McLain AquaPlus is a stainless indirect: potable water in the tank, boiler water in the coil. Cold showers with a hot boiler mean the tank sensor/drywell, DHW pump or zone valve, priority programming, or air in the coil. A side leak at the inspection plate is often a corroded drywell after a dead anode — a plate, not always a new tank. Do not treat it like a gas water heater with a pilot.
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Search Intent & The Real Problem
The Gold, Ultra, Evergreen, or GV is heating the house. The AquaPlus next to it is not heating showers — or the boiler never shuts up because the tank thinks it is always cold. Search results keep showing atmospheric gas tanks and Buderus Logalux or HTP SuperStor. Same family of machine, different sensor well and a Weil-McLain-specific failure: magnesium anode ignored, then the thermostat drywell on the inspection plate becomes the anode and rusts through. That is bulletin SB-1401, not a mystery.
If the tank is wet, use the leak page — Weil-McLain leaking. A coil inside the boiler block, not a separate tank, is a tankless coil. AquaBalance wall combis are not AquaPlus.
What other guides get wrong
They tell you to relight a pilot on a tank that has no burner. They treat every side leak as a dead stainless vessel — Weil-McLain’s own bulletin says a drywell leak is an inspection-plate job after you replace the anode. They acid-flush the coil by opening domestic faucets. And they skip DHW priority on the boiler control, which is why a “dead” AquaPlus appears every heating season when someone disabled it.
Step-by-Step Troubleshooting
Step 1: Confirm it is an AquaPlus (or PLUS), not the boiler
- What to look for: Separate insulated tank with two boiler connections (coil in/out), domestic cold/hot, a T&P, a side inspection plate with a thermostat drywell, and a side anode under a cover. Rating plate: Aqua Plus 35/45/55/80/105 and cousins. Photograph the piping before anyone “straightens it out.”
- Required tools: Phone camera, flashlight.
No separate tank and two small domestic lines into the boiler block = coil, not indirect. Combi on the wall = different product.
Step 2: Is the boiler being asked to heat DHW?
| What you see | Meaning |
|---|---|
| No DHW icon / no extra fire when you run a tap or when the tank is below setpoint | Sensor, wiring, or priority off |
| Boiler fires, DHW pump or zone valve stays shut | Output, relay, or stuck zone valve |
| Pump spinning, both coil pipes cold | Isolation valves closed or no boiler water |
| Supply hot, return hot, tank cold | Air in the coil, or no heat transfer |
| Supply hot, return cooler, tank still cold | Mixing valve or recirc stripping the tank |
| Boiler short-cycles on DHW all afternoon | Probe in the wrong well, or a failed-open call |
- What to look for: Aquastat or sensor bulb fully seated in the drywell on the inspection plate, not shoved under the jacket foam. Weil-McLain Ultra / WM97 / Evergreen DHW pair enabled. Zone valve (Taco, Caleffi, Honeywell) end switch actually closing.
- Required tools: Boiler manual for that control. Eyes on pump LEDs.
Wrong well = the control thinks the tank is always hot or always cold. I find probes under insulation at least once a month on these.
Step 3: Coil delta-T — without draining the boiler
- What to look for: Contact thermometer: coil supply from the boiler hot (often 160–180°F during a call), return cooler if the tank is taking heat. Both pipes hot and the tank cold = air or a closed coil. Both cold during a call = pump, zone, or control output. Isolation flanges closed after a filter swap is a classic spring no-heat.
- Required tools: Contact thermometer.
Purging the hydronic side is a boiler procedure at the coil vents or purge stations. Do not open domestic faucets to “bleed the coil.” Do not drop the boiler loop into a bucket unless you can refill, inhibit, and purge — that is licensed work.
Step 4: Mixing valve, recirc, and “lukewarm Weil-McLain”
- What to look for: Scald at one bath, tepid at another. Tank-out near boiler temperature, mixed-out stuck at 90°F = failed thermostatic mixer. Recirc returning into the cold inlet without a dedicated recirc port will strip the AquaPlus and keep the boiler in DHW. Someone lowered boiler water to “save fuel” and killed first-hour rating — these tanks are rated with hot boiler water, not 130°F reset all day.
- Required tools: Thermometer at tank-out vs mixed-out.
Step 5: Anode, drywell, odor, and the inspection plate
- What to look for: Weil-McLain stainless still ships a magnesium anode. Inspect at least annually (every six months in aggressive water). Chlorides over about 200 ppm eat protection. Dead anode → the steel drywell on the inspection plate corrodes and weeps. That leak is often a plate and anode, not a tank — then check the sensing bulb; wet bulbs get replaced. Rotten-egg hot water is the magnesium plus sulfate bacteria, not a gas leak. Foam jacket wet away from the plate is a vessel.
- Required tools: Correct Weil-McLain anode (it is not a generic top-mount stick on many models), licensed hands if the plate is live and hot.
Anode, drywell, and thermostat are maintenance, and Weil-McLain’s bulletin is blunt: they are not a water-quality warranty. Ignore the anode and you will be in the leak article.
When DIY Ends: Calling a Licensed Pro
Stop at boiler programming, hydronic purging, gas or oil combustion, a wet inspection plate you cannot isolate, and any coil-to-potable leak (boiler pressure dropping while domestic water discolors). You may verify isolation valves, read the control, and confirm the probe is in the well. EMS/WM parameters, zone-valve end switches, and plate replacement on a hot tank are licensed boiler work. A tech who knows AquaPlus will test the sensor, prove pump flow, combustion-check the boiler, and pull the anode before they sell you a tank. Same skill set as Buderus and SuperStor — different well.
Frequently Asked Questions
Q: Why is my Weil-McLain indirect not making hot water? A: The boiler is not getting a DHW call (sensor, drywell, or priority), the DHW pump or zone valve is dead, the coil is air-bound, or the mixing valve failed. House heat working does not prove the tank circuit.
Q: Does a leak on the side of an AquaPlus mean the tank is shot? A: Not always. A leak at the thermostat drywell on the inspection plate after a depleted anode is often a plate, anode, and bulb. A wet jacket or a pinholed coil is replacement.
Q: Can I drain the boiler to work on a Weil-McLain water heater? A: Not as a homeowner default. Isolate the coil if valves exist. Dumping the hydronic loop without a proper refill and purge takes out the boiler. Hire a licensed tech.