Signs it needs service
- Error codes on the display, especially ones related to ignition or flow
- Hot water that surges and cools during a shower
- Lower flow at hot taps than cold ones
- Unit cycling off when two fixtures run together
- Banging or whistling from the heat exchanger
The annual flush
- Shut off gas and power, close the isolation valves.
- Attach a small circulating pump to the isolation valve ports.
- Cycle descaler through the exchanger for the time the manufacturer recommends.
- Rinse with fresh water, clear the inlet filter screen and reopen the valves.
- Purge air, restart and check temperature rise and flame.
Units without isolation valves need them added before they can be flushed; it is a one-time job that makes every future service quicker.
Venting and combustion air
Home tankless heaters usually exhaust sideways through the wall in PVC or polypropylene. Snow drifts, wasp nests and lawn equipment can block terminals. We check the intake and exhaust, condensate drain and neutraliser on condensing models, and the gas supply size; undersized gas lines starve these heaters at full fire.
Error codes are listed in the manual, often on a sticker inside the cover. Note the code before resetting; it helps us bring the right part.
Is tankless right for you?
If you are weighing a switch, read our tank versus tankless guide.
What we open up on this job
| Part | Where we find it | What we do |
|---|---|---|
| Gas tank, natural draft | 40 or 50 US gal., older bungalows and splits | Thermocouple, pilot, venting and draft test |
| Power-vented tank | Common in 1990s–2000s Vaughan subdivisions | Blower, pressure switch, PVC vent check |
| Electric tank | Condos and some basement suites | Elements, thermostats, wiring at the top panels |
| Tankless combi | Newer custom homes | Descale with pump and vinegar, clean inlet screen |
Signs it is time to call
- Showers going cold sooner than last winter
- Crackle and knock from sediment as it heats
- Brown tint on the hot side alone
- A puddle forming beneath the tank
- Pilot will not stay lit
On the truck for this one
- Manometer for gas pressure
- Combustion and CO tester
- Element wrench and multimeter
- Hose for draining the tank
- Descaling pump kit
Quick answers
How often should it be flushed?
Many manufacturers suggest yearly. Harder water may call for more often.
Is gas work licensed?
Yes. Gas appliance service in Ontario requires a TSSA-registered gas technician.