 Guide to Gas-fired Hot Water Heaters - Inspection, Diagnosis, & Repair
- LP or Natural Gas Fired Water heaters: how to inspect, test, adjust, repair
- How to choose among types of hot water heaters
- No Hot water? how to get more hot water flow, quantity, performance from your water heater
- GAS WATER HEATERS, HIGH EFFICIENCY - separate article
- GAS PIPING, VALVES, CONTROLS - separate article
- Questions & Answers about gas fired hot water heaters: types, installation, troubleshooting, repairs
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Gas water heater guide: how to buy, install, inspect, troubleshoot & repair gas-fired hot water heaters. The articles at this website will answer most questions about all types of hot water heaters
as well as many other building plumbing system inspection or defect topics.
This page contains links to in-depth articles on inspecting, testing, and repairing problems residential hot water heaters of all types, including their parts, controls, and alternative sources for hot water as well as tips for improving hot water temperature, hot water pressure, and hot water quantity.
Our photo above shows an antiquated gas-fired water heater (white unit in left foreground) and just for fun, we've included an old Range Boiler water heater hidden back in the corner (silver unit behind the gas fired water heater).
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Inspection, Diagnostic, & Repair Guide to Electric Hot Water Heaters
 How do we Identify a Natural Gas or LP Gas-fired Water Heater?
The sketch at left shows the basic components of a gas-fired water heater and is provided courtesy of Carson Dunlop Associates. It's easy to identify a gas-fired water heater:
if you can find your water heater tank at all, take a look at what pipes and wires are connected to it.
A gas-fired water heater will have two water pipes connected to it (cold-in and hot out), and a pipe or in some jurisdictions a flexible copper tube bringing LP gas or natural gas to the heater.
The gas fired water heater will have a flue or "chimney" which vents combustion gases outside, either by connection to an existing chimney or flue, or in the case of power-vented and high efficiency gas water heaters, flue gases may be vented outdoors by a plastic pipe.
You'll also see a thermostat and gas valve control which combines a temperature setting with a safety device that senses the presence of a gas flame. (If there is no flame the control will turn off the flow of gas to the appliance.) Lots of newer gas fired water heaters will also include a flue gas spill switch at the draft hood atop the water heater. |
Watch out: sometimes an electric or other additional water heater is installed as an additional or backup hot water source, so you'll also want to see if you have other hot water heating equipment installed besides the first water heater that you see. Other hot water sources, such as a Tankless Coil for Hot Water, may also be present.
Gas-fired water heater Inspection Checkpoints, Defects, & Hazards List
Gas Fired Water Heater Chimney & Venting Defects
(WARNING: no inspection checklist for any topic can ever be complete or comprehensive; important water heater inspection topics may be omitted as we're working on this section. If you have comments, questions, suggestions, Contact Us.)
Our photo (left) shows an LP gas fired water heater that caught fire. This outdoor water heater installation was observed at the Ex Hacienda, Gogorron, San Luis Potosi, Mexico. The complete absence of a venting chimney on this heater may have been a factor in its poor operation. The water heater inspection dog was a volunteer.
Check for proper exhaust venting of combustion products from your gas fired water heater.
Old chimney warnings: Where a gas fired water heater is connected to a large masonry chimney it may not be able to develop sufficient draft to vent properly. The result could be dangerous spillage of flue gases into the building.
Shared flue warnings: Where a gas fired water heater shares a chimney with other heaters such as a boiler, venting of the water heater's combustion products may be unreliable, depending on whether the other larger appliance is operating or not.
Some jurisdictions do not permit sharing a flue between a gas fired appliance and other fuels such as oil; other communities may permit shared flues provided the gas vent is properly connected: usually entering the main chimney flue below rather than above the more powerfully-venting oil fired appliance.
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Short or missing gas fired water heater flue & chimney warnings
A gas fired water heater whose exhaust flue is too short may fail to develop adequate draft to vent the water heater safely and properly.
See your water heater's installation manual for the minimum allowable water heater chimney or flue height, and consider also the effects on water heater chimney draft of installations in cold or hot climates.
Outdoor Installations of Gas Fired Water Heaters
In our photo at left you can see an LP gas fired water heater installed outdoors beside a mobile home that we inspected in Monticello, N.Y. Notice (click to enlarge any InspectApedia image) that the water heater is not connected to its chimney, is installed outdoors with no protection from the weather, and is installed in a climate subject to freezing weather.
Also notice the old dead water heater leaning against its replacement. We figured that this water heater, if it's working at all, will soon join its sister. This is an improper and unsafe water heater installation. |
Even a semi-outdoor installation such as the LP gas fired water heater shown at left can have problems. This water heater (inspected in San Miguel de Allende, Guanajuato, Mexico) is installed where it is completely protected from rain.
But the water heater was not adequately protected from periodic strong winds. The clue that led to this finding was the parade of clay floor tiles stacked around the water heater bottom in a (usually successful) attempt to prevent the wind from blowing out the pilot light for this water heater.
Watch out: extreme measures to protect a gas fired (pilot light type) water heater from being blown out by wind may risk blocking combustion air - resulting in dangerous, potentially fatal carbon monoxide poisoning even at an outdoor water heater if the heater is not properly vented and is installed where its exhaust gases may enter a building. See the water heater photo just above, outside the mobile home window, for an example of this hazard. |
Blocked or missing gas water heater draft hood warning
On occasion we find items stored atop of a gas fired water heater, or as in the photo at below left, debris which has been drawn into and around the draft hood, interfering with proper water heater draft and risking unsafe venting of combustion gases from the building.
At the property where we took the photo at above left, the occupants had kept a number of large, hairy, shedding dogs in the basement utility area and their hair had clogged the water heater vent.
In our LP gas fired water heater photo shown at above right, the installer simply didn't have room for the draft hood when the water heater was installed, so he just omitted it - leaving the draft hood atop the water heater but not connected - let somebody else figure out this installation he decided.
Without its draft hood a gas fired heating appliance cannot be expected to operate properly & safely. We discuss gas appliance draft hoods further at DRAFT HOODS - gas fired.
Check for evidence of flue gas spillage at the gas fired water heater's draft hood by looking for burn marks, rust, soot or debris.
The melting pipe insulation in our photo at left indicates that flue gas has been spilling from this water heater.
The burn marks in our right hand photo show a serious flue gas venting problem with the gas fired water heater.
If flue gas spillage detection sensors (spill switches) are required in your jurisdiction they must be properly installed, usually at the gas vent draft hood.
(On some gas fired appliances such as furnaces or boilers additional sensors may be installed at or close to the gas burner as well.)
Our photo at left shows that we found a flue gas spill switch lying atop of the gas fired water heater - it had never been installed. |
Dangerous carbon monoxide warning & soot from gas appliances: If any gas fired appliance is producing soot it should be shut down immediately, inspected, and repaired before use. Soot from a gas appliance, or high levels of indoor moisture condensation that are traced to that appliance, are indicators of improper venting of combustion products and risk the production of dangerous, potentially fatal carbon monoxide gas.
Other Gas Fired Water Heater Defects
Check for proper combustion air supply for your gas fired water heater. Failure to provide sufficient combustion air is dangerous: lack of adequate combustion air will cause a gas burner to produce dangerous, potentially fatal carbon monoxide gas.
Check the pressure and temperature relief valve on your water heater: look for evidence of corrosion, leaks, improper installation, etc. A missing, modified, blocked, or leaky pressure relief valve is extremely dangerous and can lead to a catastrophic BLEVE boiling liquid vapor explosion that can cause severe damage or even fatalities at a building. See RELIEF VALVES - TP VALVES
Look for evidence of leaks in the hot water tank, or mechanical damage, or improper installation. For example most water heaters are intended to be installed in a vertical position. Installing a hot water tank horizontally or in a hole in a crawl space is likely to cause early failure of the heater, violate the manufacturer's guidelines, and may be dangerous.
Leaky water heater tanks & other leaks at water heaters
In our photo at left a gas-fired water heater is leaking.
That puddle on the floor needs investigation. Look for leaks at valves and piping around the water heater, leaks in the water heater tank itself, and look for leaks at the pressure/temperature relief valve.
Check the settings of the water heater temperature: See Temperature of Hot Water is Too Low. On a gas fired water heater the heater temperature control is usually on the gas valve itself. |
Plastic piping used for hot water distribution & connected to a water heater
In our photo at left a gas-fired water heater is connected to plastic water supply piping. The pressure rating of plastic water piping systems is usually specified in terms of the temperature as well as pressure in the piping system.
Watch out: hot water temperatures may reduce the permitted pressure rating of plastic water piping in some installations, depending on the brand and product type of plastic water piping installed. The risk is a burst water pipe, scalding, or flooding in the building.
On some plastic water piping systems you may also find a hot water expansion relief valve installed to provide added protection to the system. Details are at Water heater expansion tanks & thermal expansion safety valves
If plastic water piping is installed, such as polybutylene water supply piping, it should be at least 18" from the water heater itself. |
Look for insulation that has been improperly added to the water heater tank - it may be unsafe and may violate the manufacturer's installation instructions and warranty. See Insulate Hot Water Tank?
Check the water piping and control valves connected to the water heater for leaks, support, and for proper location of shutoff valves. An improperly installed shutoff valve on a water heater can be very dangerous, risking an explosion. Usually the "hot water tank shutoff valve" is installed only on the cold water pipe coming into the water tank (blue arrow in our photo at left)..
There should be no shutoff valve installed on the hot water line (red arrow in our photo) leaving the water tank.
Check for Gas Leaks: In addition to a characteristic odor that you may smell associated with LP or natural gas leaks, a prolonged gas leak may leave telltale dark stains on the gas piping or control. See GAS LEAK DETECTION, LP / NG for details.
Vacuum relief valves are required at water heaters in some communities, to protect against collapse of the water storage tank and to prevent backup of hot water into the cold water piping should cold water pressure drop. See this Carson Dunlop sketch of a vacuum relief valve.
Antiquated & Antique Gas Fired Water Heaters
At below left we show a working Standard Combination Gas FIred Boiler / Water Heater manufactured by Keystone Supply in Philadelphia, PA. At below right The antique gas-fired water heater shown at left is installed in the Gaudi Apartments in Barcelona, Spain. By modern standards this is an unsafe water heater.
Corrosion & leaks at water heater piping & connections
Our photo at left shows corrosion at dissimilar metals at the top of a water heater tank. When the connections at the water heater top are sufficiently rusted and corroded the heater will be un-repairable. |
Gas Water Heater Controls & Operation
Check the Sacrificial Anode & Dip Tube of Your Water Heater Tank
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The dip tube on many water heaters functions as a sacrificial anode, as we show here. By constructing the dip tube of a metal which is more readily corroded than the steel of a steel hot water tank, the anode protects the hot water tank from early failure due to corrosion. Here Carson Dunlop's sketch shows the location of the sacrificial anode on an electric water heater.
If your water supply happens to be highly conductive or corrosive (see WATER TESTING GUIDE) then the dip tub/sacrificial anode in the water tank may indeed corrode away until it leaks (dropping the hot water temperature) or disappears entirely.
If your hot water smells like rotten eggs, you should definitely check the condition of the sacrificial anode on the hot water heater, no matter what kind of water tank you've got installed.
For details of how to inspect or replace the sacrificial anode or dip-tube on a water heater, please see Water Heater Anodes & Dip Tubes |
Check the Gas-fired Hot Water Tank Temperature and Pressure Safety Relief Valve
Please see Testing the Water Heater Temperature Pressure Relief Valves
Frequently Asked Questions (FAQs)
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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