How to solve water heater installation errors

Installed in every building, water heaters are one of the most common mechanical appliances, with thousands installed every day in Canada. Installations are done by anyone from skilled mechanical contractors, to do-it-yourselfers, and anyone in between. In most cases a water heater installation is a fairly straightforward job, however as Murphy’s Law has taught us, things do not always go the way they are intended.
Modern water heaters have also added additional complications to the installation process, as water heating appliances are not nearly as simple as they once were. Condensing appliances, power burners, tankless water heaters, and plastic venting are all fairly recent changes to the water heating industry, which have brought on many new installation demands and issues that were not seen in the past. The big box store has also now put these modern water heating appliances into the hands of homeowners, many of whom do not have the necessary knowledge and skills to install the appliance correctly.
There are several common installation errors that are often seen by industry insiders; knowledgeable installers with the proper skills and tools can easily solve all of these.
One of the main problems seen in water heater tank installations has to do with thermal expansion tanks. The expansion tank is designed to alleviate the excessive pressure that can build up in the plumbing system when the water in the tank is heated and expands. Most plumbing codes now require a potable water expansion tank to be installed as part of the hot water system.
The thermal expansion tank should be installed on the cold water line above the water heater. In the past, expansion in the plumbing system was very rarely ever a problem, but the introduction of the backflow preventer has changed that. Backflow preventers are now required by many plumbing codes to be installed in the cold water supply line from the street. Before the days of backflow preventers, the expanding water in the hot water tank could push backwards into the main water supply.

Backflow preventers are now required by many plumbing codes. Credit Flexcon Industries

Now the backflow preventer does not allow that to happen and the expanding water has nowhere to go, in effect creating a “closed system.”
Water is non-compressible, so if it cannot expand when it is heated it will cause the pressure in the tank to rise, in some cases to the point where the pressure relief valve can discharge excessively, which can cause danger to occupants and water damage. Excessive water pressure can also put undue pressure on the tank heat exchanger, and can possibly crack the glass liner, which may lead to premature tank failure.
According to Brian McCabe, district sales manager for A.O. Smith Enterprises Ltd., “Expansion tanks are a huge problem in the industry. Expansion tank issues are primarily related to under sizing, and lack of set-up.” He claims that “many installers do not properly size the expansion tank, so it is often not capable of doing the job.
“Expansion tanks are often installed without any attention paid to the set-up requirements. “The expansion tank should be set-up when it is installed to ensure it is pressurized properly to match the system. This set up is often not done by the installer,” adds McCabe. The pre-charge pressure of the tank should equal the incoming water pressure. Tanks are typically factory pre-charged to 40 PSI, so if a different pressure is required, use a bicycle pump or air compressor to add air to the tank via the charging valve.
With the rising popularity of tankless instantaneous water heaters, another installation problem that is often seen is undersized natural gas pipe line sizing. According to Leo Vaillancourt, a former trainer with Navien, “The most popular sizes of tankless units are in the 180 to 199 MBH size range. With these sizes of units the customer can get the three to four gpm of DHW flow rate that is required for most modern homes.”
In the retrofit market, the tankless unit is often replacing a 40 or 50 gallon storage tank that had a 36 to 48 MBH capacity.
“This high BTU output requirement for the tankless means that a much bigger gas line is now required to satisfy the unit. There are many instances where the existing gas line is left in place, which is simply not big enough for the new tankless unit,” says Vaillancourt.
In most cases a new bigger gas line must be installed to ensure that the tankless will operate properly. Vaillancourt says that “some new tankless units utilize negative pressure gas valves, which allow them to operate with gas pressures as low as three inches w.c.” This feature can help to alleviate some minor under-sizing issues, however it still does not solve all problems and will often not be enough to overcome a severely undersized NG pipe.
Modern tank type and tankless water heaters also suffer another common problem related to the lack of proper burner set up. Power burners that require precise gas-air ratios are the norm for many units now. According to Vaillancourt, tankless units are now “finely-tuned machines that require some basic set up or they won’t run properly.”
“Many tanks now have power burners, which are a lot less forgiving than the old units with atmospheric burners. If not set up correctly the result can be hard starts, burner lift-off, and noisy operation,” says McCabe. If left unchecked, these issues can result in more stress on heat exchanger and shorter lifespan.
Both Vaillancourt and McCabe say that it is not uncommon for the installer to install the unit, then fire it up and walk away. As long as the unit is running, they will not do any further checks. Both agree that a few basic calibrations are essential to ensure a problem free operation of the unit. These include checking the incoming gas pressure with a manometer to ensure it is in the proper range specified by the manufacturer, and measuring the flue gases with a combustion analyser to check the CO2 percentage. With these checks problems can be detected and adjustments made to correct burner issues before they cause operational issues.
High efficiency condensing water heaters now use special high temperature plastics for venting, and are commonly exhausting flue gases through the side wall of the building. Venting installation errors are frequently seen which cause some serious operating issues. In Vaillancourt’s experience “It’s amazing how many things can get messed up with the vent!”

Every water heater manufacturer publishes the maximum equivalent vent length that can be used with their equipment. This length is primarily based on the capacity of burner fan motor to overcome resistance from the venting, and from external wind forces. It is not uncommon to see installers put in vents that are too long or have too many elbows.
When stuck with the choice of moving the water heater to a new location to accommodate the vent limitations, or stretching the vent length a few more feet, installers often take the easy way out and just add more vent pipe. Surely a couple of extra feet won’t be a problem! This is often a bad choice.
Extra venting adds extra resistance that the blower may not be able to overcome. This often causes the burner to shut down or lock out, with the problem sometimes not showing up until a very windy day.
Another common venting issue is improper venting slope. A vent pipe should always slope backwards towards the appliance so that any condensate liquid can drain back to the unit and be disposed through the unit’s condensate drain line. A vent that is not properly sloped can create a trap where condensate can build up and block the vent. Any condensate sloped towards the outdoors can cause ice formation problems.
This lack of proper slope can be caused by not paying enough attention during installation, or from improper or broken pipe supports. Either way a blockage can occur, resulting in another burner lockout and another service call.
Soldering directly to fittings on a water heater is another error that can cause some serious problems. Damage to plastic components of the unit can result, especially to plastic dip tubes on many tank type heaters. Instead of soldering directly to the unit, prep the fittings on the floor or a fireproof level surface. Allow fittings to cool before making the remaining solder connections further from the unit. It can also help to wrap a cold wet rag around the copper pipe you are soldering to prevent heat from conducting to the unit.
Premature activation of electric elements or gas burners prior to completely filling a tank is probably the final issue to avoid. Whether done accidentally or because someone was in a rush to finish up, a dry fired tank can result in serious damage to electric elements or possibly cracking the glass lining of the tank. Make sure all the air is completely purged from the tank by opening a faucet and running the water until all the air is gone.
With government efficiency requirements climbing all the time for new water heaters, we can expect water heating appliances to continue to change and evolve. Taking the time to learn about the installation requirements for new equipment will always pay dividends for contractors by reducing installation problems and service calls. Attention to detail during the installation of a water heater will always result in more efficient operation, fewer nuisance callbacks, longer service life, and more satisfied customers.

Robert Waters is president of Solar Water Services Inc., which provides training, education and support services to the hydronic industry. He is a mechanical engineering technologist graduate of Humber College and has over 30 years experience in hydronic and solar water heating. He can be reached at solwatservices@gmail.com.