Gas-fired tanks, diagnosed properly
Gas Water Heater Repair in Denver, CO
Pilot outages, burner trouble, sooting and draft problems have a handful of causes. We test rather than guess — and we check combustion before we leave.
- Standing pilot and electronic ignition
- Draft and CO safety check included
- FVIR screen cleaning
- Atmospheric, power-vent and direct-vent
Gas water heaters are the most common type in Denver's housing stock, from 1920s bungalows in Baker with a shared chimney to 2005 builds in Green Valley Ranch with a dedicated B-vent. They are simple machines with a short list of failure points — which means a technician with a manometer, a millivolt meter and a draft tester can pinpoint the fault in about twenty minutes instead of selling you a tank.
The faults we find most often
- Pilot lights, then dies on releaseClassic thermocouple failure. A healthy thermocouple produces roughly 25–30 millivolts; below about 18 the gas valve's magnet drops out. Replacement is quick and inexpensive.
- Pilot will not light at allDirty or spider-webbed pilot orifice, no gas at the valve, or an air-intake screen at the base clogged with lint and dust — extremely common where the heater shares a laundry room.
- Burner lights then shuts off in a few minutesBlocked flue, a collapsed vent connector, or a downdraft — the flame-rollout or thermal switch is doing its job. This is a safety fault, not a nuisance.
- Soot on the burner or draft hoodIncomplete combustion from insufficient combustion air, an obstructed vent or an incorrect orifice. Never ignore sooting: it points toward carbon monoxide production.
- Burner is noisy or has yellow, lazy flamesDirty burner ports, dust in the air intake, or combustion air starvation. A correct flame is mostly blue and stable.
- Unit heats slowly and the flue is hotHeavy sediment insulating the tank floor from the burner — heat goes up the flue instead of into the water.
- Gas control valve clicks but no flameFailed control valve or a wiring fault on electronic ignition models.
Draft, combustion air and altitude
This is where Denver differs from most of the country, and where most quick swaps go wrong. At 5,280 feet the air carries meaningfully less oxygen per cubic foot than at sea level. An atmospheric water heater relies entirely on buoyancy to pull combustion gases up the flue, and that buoyancy is weaker in thin air.
Now add what has happened to Denver homes over the last two decades: new windows, spray foam, sealed rim joists, powerful range hoods and high-CFM bath fans. A basement that drafted fine in 1998 can go negative when the dryer and the furnace run together, and the water heater flue becomes the easiest path for makeup air — pulling combustion products back into the house.
Our standard test is worst-case depressurization: close the basement, run the dryer, furnace and every exhaust fan, then smoke-test the draft hood. If it spills, the fix is combustion air — a transfer grille, a dedicated intake, or a change to a power-vent or direct-vent unit that does not depend on natural draft at all.
Every home with gas appliances should have working carbon monoxide alarms on each level and near sleeping areas. Colorado law has required CO alarms in homes with fuel-fired appliances since 2009. Test them when you test smoke alarms.
Atmospheric vs power-vent vs direct-vent
| Type | How it vents | Where it suits | Failure points |
|---|---|---|---|
| Atmospheric | Natural draft up a B-vent or lined chimney | Basements with an existing flue | Draft spillage, blocked flue, FVIR screen clogging |
| Power-vent | Blower pushes exhaust out a sidewall in PVC | Finished basements, no usable chimney | Blower motor, pressure switch, condensate line |
| Direct-vent | Sealed intake and exhaust through one wall assembly | Tight, air-sealed homes and confined closets | Termination blockage — snow and nests |
What repair costs on a gas unit
| Repair | Typical Denver range |
|---|---|
| Thermocouple or flame sensor | $150–$280 |
| Pilot assembly / burner clean and FVIR screen | $180–$340 |
| Thermostat / gas control valve | $350–$650 |
| Vent connector re-pipe or draft correction | $250–$700 |
| T&P relief valve | $150–$280 |
| Full sediment flush | $140–$250 |
Frequently asked questions
Why does my gas water heater pilot keep going out?
In order of likelihood: a weak thermocouple, a dirty pilot orifice, a clogged air-intake screen at the base of the tank, or a downdraft in the flue. A thermocouple that reads under about 18 millivolts under load needs replacing regardless of how it looks.
Is a yellow flame on my water heater dangerous?
It is a warning sign. A correct burner flame is predominantly blue and steady. Yellow, lazy or lifting flames indicate incomplete combustion, which produces carbon monoxide. Shut the unit off and have it checked before running it again.
Can I relight the pilot myself?
On most units, yes — the instructions are printed on the tank. If it will not stay lit after two attempts, stop. Repeated attempts flood the chamber with unburned gas. That is the point to call.
Does Denver's altitude affect my gas water heater?
It affects combustion and draft. Most residential units are certified for installation up to roughly 10,100 feet without modification, but thinner air plus a tightly sealed home makes draft spillage more likely, which is why we smoke-test under worst-case conditions on every gas call.
What is the screen at the bottom of my water heater?
The FVIR (flammable vapor ignition resistant) air-intake screen, required on units built since 2003. It keeps flammable vapors out of the burner chamber — and it clogs with lint, pet hair and dust, which starves the burner. It should be cleaned at every annual service.
Cold shower this morning? We can be out today.
Tell us what the heater is doing and we will give you a straight answer on the phone — repair, replace, or wait.