Phase III Indirect Water Heater Troubleshooting

The Short Answer: Phase III is a Triangle Tube product name. Most Phase III heaters in homes are TR, HL or SMART series indirect tanks: a stainless domestic tank inside a jacket of boiler water. They have no burner or element of their own. Most hot-water complaints therefore trace to the boiler, its circulator or controls, the tank’s thermostat, or plumbing around the tank.

Confirm which Phase III you have

Read the label on the tank. Triangle Tube’s Phase III troubleshooting guide (opens in a new tab) covers all Phase III indirect heaters: the TR series, the SMART series and the older HL series. Triangle Tube also sold a Phase III HM series. Its HM manual (opens in a new tab) describes a larger oil- or gas-fired heater with its own power burner, rated from 165,000 to 390,000 Btu/hr. An HM unit is a fuel-burning appliance, and the indirect-tank advice below does not apply to its burner.

Triangle Tube’s Phase III products are home and commercial water heaters, not RV appliances.

How a Phase III indirect tank works

The domestic water is in an inner stainless tank. Boiler water circulates through the outer tank around it. The installation and maintenance guide (opens in a new tab) calls these the inner (domestic water) tank and the outer (boiler water) tank. A thermostat (aquastat) with a sensing bulb in a drywell calls the boiler for heat. The boiler then fires and a circulator or zone valve sends hot boiler water through the outer tank.

Two consequences matter for troubleshooting:

• If the boiler, circulator, zone valve or wiring does not respond, the tank cools, even though nothing is wrong with the tank.
• A leak in the inner tank can push domestic water into the boiler loop. That usually shows up as rising boiler pressure or a dripping boiler relief valve, not as a puddle under the tank.

Symptoms and likely causes

What you can check safely

• Is the boiler on? If the house heat works but hot water does not, note that for the technician. If neither works, the problem is likely with the boiler, not the tank.
• Read the boiler pressure gauge and write down the number. Do not add water or release pressure yourself. The guide notes a typical system pressure of about 12 psig after venting.
• Check the tank thermostat knob. The manual says it is factory-set to its lowest temperature, which may not suit your needs. Turning it up modestly is an owner adjustment. Check the water at a tap afterward; Triangle Tube cites the Consumer Product Safety Commission recommendation of 130°F or less.
• Think about what changed. The guide gives the example of a new bathroom or whirlpool tub, or higher-flow shower heads, that the tank was never sized for.
• Watch the T&P discharge pipe. The guide suggests a homeowner can place a bucket under it for a day or two to confirm whether it is the source of water.
• Look for leaks. The manual’s monthly owner tasks include visually checking valves, pipes and fittings for leaks, and calling a technician for any repair.

Do not drain the tank yourself. The manual warns that boiler-side pressure must be below 15 psig before the inner tank is drained, and the outer tank drained first. Draining the domestic side with the boiler loop still under pressure can damage the inner tank.

What the technician will check

Triangle Tube’s guide directs the technician to:

• confirm that the boiler actually fires and the circulator or zone valve opens when the tank calls for heat;
• test the tank thermostat;
• check that the sensing bulb fits snugly at the right depth in its drywell;
• inspect the dip tube;
• compare boiler output with the household’s demand;
• check the boiler temperature, piping size and air in the loop.

For excess temperature, they may lower the boiler temperature, reposition the sensing bulb, or fit a thermostatic mixing valve. The manual says the boiler limit should be at least 20°F above the tank thermostat setting and never above 210°F.

For relief-valve problems, they size and check the expansion tanks; the boiler-side tank must allow for the extra boiler water held in the outer tank. They also check the incoming water pressure; the guide recommends a pressure-reducing valve above 70 psi. If an inner-tank leak is suspected, they isolate the tank from the boiler loop and watch whether the boiler pressure stops rising.

Repair or replace

Thermostats, drywell seals, dip tubes, relief valves, expansion tanks, circulators and zone valves are part repairs. A confirmed leak in the inner or outer tank means replacing the water heater. When you call for service, have both the tank model and the boiler make and model ready; the guide tells technicians to know both before the visit.

For Triangle Tube’s other water-heating products, including its combination boilers, see Triangle Tube water heater problems. A dripping tank relief valve is covered in more depth in pressure relief valve leaking on a water heater and expansion tank full of water.

Frequently Asked Questions

Q: Who makes Phase III water heaters? A: Triangle Tube. The name appears on its TR, HL and SMART indirect tanks and on the separate HM oil- and gas-fired series. Use Triangle Tube documents that match the series on your label.

Q: Why is my hot water scalding after several short uses? A: Triangle Tube’s guide calls this stacking. Small, repeated draws trigger heating calls without emptying the tank, so the top layer can approach boiler temperature. Lowering the tank setting helps. A technician can also lower the boiler temperature or fit a mixing valve.

Q: My boiler relief valve keeps dripping. Could the water heater be the cause? A: Possibly. An undersized or waterlogged boiler expansion tank is the more common cause. A leak in the inner tank can also push domestic water into the boiler loop. A technician tells the two apart by isolating the tank and watching boiler pressure.