Amtrol BoilerMate Indirect Water Heater Problems
On this page (7 sections)
The Short Answer: An Amtrol BoilerMate has no burner or element of its own. It heats water with boiler water pumped through a coil inside the tank, so most “no hot water” problems are in the boiler, the circulator or zone valve, the control, or air in the coil. Amtrol’s own troubleshooting chart starts with power, the circulator and the boiler, then moves to a fouled heat exchanger.
How a BoilerMate works
When the BoilerMate’s control senses the stored water has cooled, it calls the boiler and starts a circulator (or opens a zone valve) that pushes hot boiler water through the coil in the tank. The boiler water and your tap water never mix. That means a working boiler is necessary but not enough: heat also has to reach the tank. If your home’s radiators are hot but the tap is cold, the problem is almost always in the tank’s own zone.
Match the symptom to the likely cause
The table follows the troubleshooting chart in Amtrol’s BoilerMate installation and operation instructions (opens in a new tab).
| What you notice | Causes Amtrol lists | Urgency |
|---|---|---|
| No hot water at all | No power to the unit, air-bound circulator, failed circulator or zone valve, failed control, boiler not running | Moderate |
| Hot water runs out quickly | Demand exceeds capacity, setpoint too low, boiler cannot supply heat and hot water at once, fouled heat exchanger, poor flow through the coil | Low to moderate |
| Water too hot | Wrong boiler piping, setpoint too high, temperature sensor not fully inserted, stuck zone valve, check valve stuck open | High: scald risk |
| Relief valve dripping or opening | Missing or undersized expansion tank, wrong expansion tank charge, city pressure too high, overheating, faulty relief valve | Moderate |
| Boiler will not run on a hot-water call | Wiring, boiler high limit, control’s post-purge set too high, boiler fault | Moderate |
Digital control error codes
BoilerMate models with Amtrol’s digital control can display three diagnostic errors. Amtrol’s manual describes them this way:
- Temperature sensor fault. The thermistor is unplugged or damaged.
- Overheating. Hot water has exceeded the maximum setpoint. Causes include an error in the boiler piping, a zone valve stuck open, or a leak in the sensor well.
- Slow heating. The tank has taken more than 60 minutes to reach setpoint or cannot reach it. Causes include faulty equipment, a fouled heat exchanger, or no fuel.
Amtrol says the codes clear on their own when the cause is corrected, or can be reset by switching power to the control off for 5 seconds. An overheating code is the one not to clear and ignore: test the water at a tap before anyone bathes.
What you can check safely
- Is the boiler running and heating the house? If the boiler is off or locked out, the BoilerMate cannot heat. Check the boiler’s emergency switch and breaker, which Amtrol lists first.
- Is the control on and set correctly? The digital control’s default setpoint is 120°F and its range is 90 to 150°F. Look for a setpoint someone lowered or an error code on the display.
- Did the problem start after boiler work? Draining or refilling the boiler is a common time for air to get trapped in the coil’s loop.
- Is it worse when the heat is on? If hot water runs short only in cold weather, the boiler may be unable to keep up with both loads. Amtrol’s control has a priority setting for this, which your heating contractor can enable.
- Is the relief valve on the tank dripping? Note whether it happens after hot-water use. Never cap or plug it.
What the heating technician will check
The technician checks that the control calls for heat and that the circulator or zone valve responds. They purge air from the coil’s loop following Amtrol’s procedure, which involves isolating and flushing the boiler return line. To check for scale, Amtrol has them compare boiler supply and return temperatures during a cold start: a difference of less than 20°F points to a fouled heat exchanger that needs cleaning, and water treatment to prevent it returning.
For a dripping relief valve, they check the thermal expansion tank’s size and air charge against the home’s water pressure, and Amtrol calls for a pressure-reducing valve if city pressure is over 80 psi. Background on why that matters is in A. O. Smith’s thermal expansion bulletin (opens in a new tab) and our guide to an expansion tank full of water.
Repair or replace
Controls, sensors, circulators, zone valves, relief valves and coil cleaning are all repairs. Amtrol sells replacement heat exchangers for CH models. A leak from the tank itself, with fittings and the relief valve dry, means the tank needs replacing. Other indirect brands are covered in SuperStor indirect problems and Buderus indirect problems.
Frequently Asked Questions
Q: Why did my house lose heat while the BoilerMate was heating? A: With priority mode on, space heating waits until the tank reaches setpoint. Amtrol notes that a failed circulator or thermostat can delay space heating indefinitely in that mode, which risks frozen pipes in winter. If the house stays cold, call for service promptly.
Q: Can antifreeze go through a BoilerMate coil? A: Amtrol says glycol should only be used with double-wall heat exchanger models, so that a coil leak is unlikely to contaminate drinking water. Check your model number before adding antifreeze to the boiler system.
Q: How should a BoilerMate be drained? A: Amtrol warns that draining without shutting off the supply valve and opening the relief valve or a downstream fixture can damage the tank’s liner, and recommends a vacuum breaker. Draining is usually done during service; see how to drain a water heater with no floor drain for the general approach.
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.
- Amtrol BoilerMate indirect-fired water heaters: installation and operation instructions (opens in a new tab)Amtrol BoilerMate CH-series indirect water heaters with digital or mechanical controls.
- 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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