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Tankless service and repair
Tankless Water Heater Repair in San Diego, CA
Error codes, cold sandwiches, scale build-up and units that cut out mid-shower — diagnosed and repaired at your home.
If your tankless water heater is throwing an error code, running cold after a minute, or short-cycling between hot and cold, it usually needs servicing rather than replacing. Blue Planet Plumbing repairs tankless units across San Diego County — we read the fault code, test the gas and water side, check the heat exchanger and flow sensor, and tell you what the unit needs before any work starts.
Why a tankless unit stops making hot water
A tankless heater only fires when it senses flow, so most faults show up as heat that arrives late, disappears part-way through a shower, or never arrives at all. The three common causes we find are mineral scale narrowing the heat exchanger, a gas supply that cannot deliver enough volume when the burner steps up, and a flow sensor or filter screen that has silted up.
Scale is the most common of the three in San Diego. Hard water leaves deposits inside the exchanger, the unit has to work harder to reach the set temperature, and eventually it protects itself by shutting down. That is a service job, not a replacement — the exchanger is flushed and the inlet screen cleaned, and the unit goes back to full output.
The second pattern is the cold-water sandwich: hot, then a slug of cold, then hot again. That is normal on short draws, but if it lasts more than a few seconds every time, the unit is either undersized for the fixture group or the recirculation setup needs adjusting.
What we check on a tankless repair visit
We start at the display. Modern units log a fault code, and the code narrows the fault to a system — ignition, flame sensing, venting, flow or overheating — before anyone opens the cabinet. From there we test the incoming gas pressure under load, because a unit that lights fine at idle and fails at full burn is almost always starved of gas rather than broken.
Then we look at the water side: inlet filter screen, flow sensor, isolation valves and the condition of the heat exchanger. If the unit has never been flushed, we descale it. If a component has failed, we tell you the part and whether it is worth fitting against the age of the unit.
Venting gets checked last. A blocked or badly terminated flue trips the same safety cut-outs as an overheating exchanger, and it is the one fault where the right answer is to stop the unit until it is corrected.
Repair or replace: how we decide
We would rather repair a unit that has life left in it. A heater that needs a descale, a flow sensor or an igniter is worth fixing. A heater with a failed heat exchanger, a cracked manifold, or a fault list that keeps growing is usually a replacement conversation — and we will say so rather than sell you a repair that buys a month.
If replacement is the right call, our tankless water heater and water heater pages cover the options, and we can quote the swap on the same visit.
Brands we service
We work on the units San Diego homes actually have on the wall — Navien, Takagi, Noritz, Rinnai and Rheem among them. Our project log includes Takagi warranty work in Poway, Noritz servicing in Chula Vista, Navien installations in Chula Vista and Clairemont, and tank-to-tankless conversions in La Mesa and Spring Valley.
Brand matters mostly for parts and fault codes. The diagnostic approach — gas, water, venting, controls — is the same whatever badge is on the cover.
Symptom, likely cause and what the visit involves
| What you notice | Likely cause | What we do |
|---|---|---|
| Error code on the display | Logged fault in ignition, flow, venting or overheat | Read the code, test that system first |
| Hot then cold then hot | Cold-water sandwich or recirculation set-up | Check sizing, flow rate and recirculation settings |
| Water runs warm, never hot | Scale in the heat exchanger or low gas volume | Descale the exchanger, test gas pressure under load |
| Unit cuts out mid-shower | Overheat cut-out or blocked inlet screen | Clean the screen, flush the exchanger, check the flue |
| No ignition at all | Igniter, flame sensor or gas supply | Test ignition circuit and gas, replace the failed part |
| Rumbling or kettling noise | Heavy mineral build-up inside the unit | Full descale and inlet filter clean |
| Water pressure dropped at hot taps | Silted inlet filter screen | Remove and clean the screen, check isolation valves |
Tankless water heater repair FAQs
Why does my tankless water heater keep going cold?
Most often the heat exchanger has scaled up, so the unit cannot reach its set temperature and shuts down to protect itself. The other common cause is a gas supply that cannot keep up when the burner steps to full output. Both are diagnosed on the visit — we read the fault code first, then test the gas and water side before opening the cabinet.
What does the error code on my tankless heater mean?
Every manufacturer logs faults by system: ignition, flame sensing, flow, venting or overheating. The code will not tell you which part failed, but it tells us where to start, which is why we always read it before doing anything else. If the display is blank, that is usually power or the control board.
How often should a tankless water heater be flushed?
San Diego water is hard, so units here scale faster than the manufacturer literature assumes. If yours has never been descaled and it is more than a couple of years old, that is the first thing to look at. We flush the exchanger and clean the inlet screen as part of a service visit.
Can you repair my tankless unit or does it need replacing?
If the fault is scale, a flow sensor, an igniter or a filter screen, it is worth repairing. If the heat exchanger itself has failed, replacement is normally the better call. We tell you which it is before starting, and if it is a replacement we can quote the swap on the same visit.
Do you work on Navien, Takagi and Noritz units?
Yes. Those three plus Rinnai and Rheem are the units we see most across San Diego County. Our project log includes Takagi warranty work in Poway, Noritz servicing in Chula Vista and Navien installations in Chula Vista and Clairemont.
My hot water pressure has dropped — is that the heater?
It can be. The inlet filter screen on a tankless unit silts up over time and chokes the flow before the water ever reaches the burner. It is a quick check and a quick clean, and it is worth ruling out before anyone starts looking at the pipework.
Related pages: tankless water heaters, water heaters, plumbing in Poway, Chula Vista plumbing, and emergency plumbing services if you have no hot water at all.
Book a tankless repair visit
Tell us the make and the error code if you have one, and we will come out with the right parts on the van.
If the unit is at the end of its life rather than faulty, tankless water heater installation in San Diego covers sizing, gas supply and venting for a replacement.
