Water Heater
Storage, tankless and heat pump water heaters, and the safety devices every installation depends on.
Safety
What it is
A water heater raises the temperature of domestic hot water and, in storage types, keeps a volume of it ready. The main families are gas or electric storage, tankless, indirect fired from a boiler, and heat pump water heaters.
| Type | How it heats | Notes |
|---|---|---|
| Gas storage | Burner under a tank with a flue through the centre | Needs venting and combustion air |
| Electric storage | Upper and lower elements with thermostats | Simple, slower recovery |
| Tankless | Heats on demand as water flows | High input, needs specific gas sizing and venting, has a minimum flow rate |
| Indirect | Boiler water through a coil in a tank | Recovery depends on boiler capacity |
| Heat pump | Moves heat from surrounding air into the tank | Cools and dehumidifies the space it sits in, needs adequate air volume |
Safety devices
- Temperature and pressure relief valve, with a discharge pipe run as required and never capped or plugged.
- Thermostat and high limit, with manual reset on electric units.
- Flammable vapor ignition resistant design on many gas units.
- Anode rod, which protects the tank from corrosion and is a maintenance item, not a safety device.
- Expansion tank on systems with a check valve or pressure reducing valve, where thermal expansion has nowhere to go.
Scald risk and relief valves
What can go wrong
| Symptom | Common causes |
|---|---|
| No hot water, gas unit | Pilot or ignition failure, gas supply, thermocouple, gas control valve, blocked vent |
| No hot water, electric unit | Tripped high limit, failed element, failed thermostat, open breaker |
| Not enough hot water | Undersized tank, dip tube failure, one element out, high demand, crossover through a mixing valve |
| Relief valve dripping | Thermal expansion with no expansion tank, high supply pressure, or a failed valve |
| Rumbling or popping | Sediment buildup on the tank bottom |
| Water around the base | Tank corrosion failure, relief discharge, or a fitting leak |
Local requirements
Venting, combustion air, relief discharge piping, seismic strapping, expansion control, permits and maximum delivery temperature requirements vary by jurisdiction, adopted code edition and the manufacturer instructions.
Local Code Notice
Symptoms
Practice & Mastery
- Questions1
- Water Heater Troubleshooting Scenarios2
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