Plumbing and heating expert Richard Trethewey helps a homeowner solve a hot water shortage problem. Thinking that they had an on-demand water heater, the homeowner couldn’t understand why the water from the tub spout would cool before the tub would fill. Richard discovers it’s a combi unit with a water tank and helps the homeowner solve the problem by installing a reserve tank.
Folks who have an on-demand water heater and find that their tub faucets are running cold before the tub fills might be suffering from a water flow issue. Almost all fixtures in a home are regulated to allow no more than 2.5 gallons of water per minute, and most on-demand heaters can handle that. However, tub faucets are not required to meet those regulations, and they can drain hot water faster than a water heater can produce it. The answer? A hot water reserve tank, and here’s how to install one.
How to Install a Reserve Tank
- Start by turning off the power and gas to the combi boiler or on-demand water heater. Drain the water out of the combi boiler’s tank with the hose and bucket.
- Cut the piping that runs from the boiler’s tank to the system, and then cut the return side so you can tap the reserve tank’s outlet into the system.
- Install a new expansion tank between the boiler’s tank and the new reserved tank. Make sure to use pipe dope on any threaded fittings.
- Connect the tank’s outlet pipe to the reserve tank’s inlet. Install a bronze pump on the outlet side of the reserve tank and connect the reserve tank to the return side of the system.
- Slowly turn on the water to purge the air from the boiler. Open a faucet valve and keep it open until water flows continuously without hissing or burping.
- Turn the combi boiler back on. Let it heat and circulate the water through the reserve tank.
Richard Trethewey helps a homeowner understand how different flow rates in water fixtures could be the culprit behind a bathtub that turns cold after only being halfway filled.
Richard discovers the tankless water heater can’t keep up with the tub spout’s flow rate. He suggests installing a separate 80-gallon reserve tank that can easily handle the 60-gallon soaker tub. With the assistance of a plumbing specialist, an ideal location for the new unit is identified. Richard suggests an area near the existing tank that isn’t prone to freezing.
After disconnecting the electrical supply, connect the tankless inlet to a bronze or stainless steel
circulator. On the tank, tankless outlet, use both thread tape and pipe dope and connect a 3/4 inch tube adapter and connect this to the hot tankless coil outlet on the boiler. Use both thread tape and pipe dope to connect a 3/4 inch NPT brass tee. In the run of the brass tee, install a 3/4 inch NPT brass T-long element for hot water heaters, as required by local codes. In the bottom of the tee vertically down, install a 3/4 inch NPT x 3/4 inch tube adapter.
Then install two 3/4 inch sweat street 90-degree elbows. Fill the storage tank by opening the cold water shut-off valve. Make certain any drain valves are completely closed. Purge air from the system by opening a hot water outlet at a fixture in a kitchen or bathroom.
When water flows freely from the outlet, the system is purged. Set the storage tank to the desired
temperature. Boiler high limit should be set at least 20 degrees F higher than the storage tank temperature setting.
Water heater products were manufactured by Heat Transfer Products (HTP) and Jomar Distributors.
Expert assistance provided by Papalia Home Services.
- Reserve tank
- Expansion tank
- Thread tape
- Pipe dope
- Bronze pump
- Copper piping and fittings (press or push to connect)