Hey, it’s Mike. I’m a licensed gas fitter who’s been fixing tankless units all over Peel Region for the last 12 years. If your Rinnai, Navien, Noritz, or Rheem on-demand heater is acting up in Mississauga, Brampton, Oakville, or anywhere in the GTA, this is the no-BS guide I wish every customer read before calling.
I’ve crawled under way too many Mississauga houses in February to know precisely what goes wrong with these things: hard water, freezing pipes, power surges from summer storms, you name it. Here’s the real scoop from someone who’s actually holding the wrench.
Most Common Tankless Problems I See Every Week in Mississauga
When you have no hot water whatsoever with error code 11 or 12 blinking, water growing cold partway into a shower, noises that seem to be banging or whistling, or the unit is turning off with such codes as 10, 16, 29 or LC, the problem is most likely to be typical tankless water heater issues. Leaks at the bottom of the pressure-relief valve and a lower volume rate, in which you hardly manage to get a hot shower despite the unit being switched on, are also common signs. In 9 out of 10 cases, the cause is one of six things: ignition failure, scale deposits (and hard water in particular), dirty filters, frozen condensate lines in winter, a faulty flow sensor, or a defective circuit board.
The One Thing That Saves Me Hours on Every Call (your single bullet paragraph)
90 % of “my tankless is broken” calls turn out to be part of a 10-minute fix once I clean the inlet water filter and descale the heat exchanger. Most homeowners have never even opened the front cover to look.
Quick-Look Table of Common Error Codes & What They Usually Mean in Mississauga Homes
| Brand | Error Code | What It Usually Is in Our Area | Typical Fix Time (if parts in truck) |
| Rinnai | 10 | Air supply or exhaust blockage (dryer vent lint, bird’s nest, ice) | 30 to 60 min |
| Rinnai | 12 | Flame failure, dirty flame rod, or low gas pressure | 20 to 45 min |
| Navien | E003 | Ignition failure (same as above) | 30 to 90 min |
| Navien | E016 | Overheating because of scale (super common here) | 2–3 hrs with descale |
| Noritz | 11 | No ignition usually needs flame rod cleaning | 20–40 min |
| Rheem | 29 | Condensate drain blocked (freezes solid in winter) | 45–90 min |
| Any brand | LC / 90 | Lime/calcium buildup (Mississauga water is brutal) | Full flush needed – 2 hrs |
If your unit is flashing one of these, don’t panic – most are totally fixable the same day.
Signs You Should Call for Tankless Repair Right Now (Don’t Wait)
I get it, nobody wants to spend money if it’s “kind of” working. But here’s when you’re just making it worse:
- Water smells burnt or metallic
- You hear a kettle-like boiling sound inside the unit
- The pressure-relief valve is dripping constantly
- Hot water takes forever to arrive (could be a clogged filter)
- Unit is over 10 years old and has never been descaled (you’re living on borrowed time)
Waiting usually turns a quick repair into a new heat exchanger or circuit board.
Winter Is Brutal on Tankless Units in Mississauga – Here’s Why
Our cold snaps + high humidity = condensate lines freezing solid overnight. I do more emergency calls in January and February than the rest of the year combined. If your unit is in an unheated garage or on an outside wall, you’re at risk. A $30 heat tape wrap or moving the condensate line inside can save you a midnight cold-shower panic.
How to Pick a Legit Repair Tech in Mississauga (Not Some Fly-by-Night Guy)
A couple of questions or so when it comes to selecting a technician, and you are playing lotto. They must present a TSSA gas technician license (G1 or G2) and an appropriate tankless endorsement, and possess a legitimate manufacturer authorization for your brand, i.e., Rinnai Pro or Navien Service Specialist certification. A properly prepared tech is expected to show up with a truck equipped with standard parts such as flame rods, flow sensors, igniters and gaskets. Reputable companies always offer same-day or next-day services even during winter when they are busy. Make sure there are authentic Google reviews over the last few months, preferably with pictures of their vans and licenses. There are a few local companies that have always done it right, namely Dr HVAC, Convertible Heating, Laird and Son, Peel Plumbing, and a few old habits of one-man operations.
Simple Maintenance You Can Do Yourself Between Visits
- Turn off the power/gas and clean the inlet water filter every 6 to 12 months (it’s literally a little screen that takes 5 minutes).
- Check the air intake filter (looks like a furnace filter), vacuum it if it’s dusty.
- Look at the clear condensate hose in winter; if it’s frozen, carefully pour warm water over it.
- Run a descale every 1 to 2 years if you have hard water (or get the tech to do it).
Ready to Get Your Hot Water Back Today?
If your tankless is throwing error codes, making weird noises, or just not keeping up with your teenagers’ showers anymore, don’t suffer through another cold morning.
Pick up the phone and call a real TSSA-licensed tech who actually carries parts for Mississauga homes. Most good companies can have someone at your door in a few hours (especially if you say it’s an emergency, no hot water counts!).
Stop googling error codes at 6 a.m., get it fixed properly once and enjoy endless hot water again.
Reach a legit local company right now while you’re thinking about it. Your future warm shower is waiting.
