Why Is My Boiler Running but the House Is Still Cold? A LaPorte Guide

The Gauge

What Your Boiler Pressure Gauge Should Say, and Why Height Matters

A closed hot-water heating system is a column of water, and water has weight. As PHCP Pros sets out in its Radiant Insider column, every foot of height adds about 0.43 psi at the bottom of the system. A typical two-story house with baseboard and the boiler in the basement has a system about 16 feet tall, so it takes roughly 7 psi at the boiler just to push water to the top. At 7 psi the gauge in the basement shows pressure, but the pressure at the highest radiator is zero.

That is why about 12 psi is the common cold setting for that house: the extra 5 psi keeps positive pressure at the top. It matters because at zero, and for a moment below zero when the circulator starts, automatic air vents at the high points can let air in instead of pushing it out. The air collects at the highest radiators or baseboard until they airlock and give no heat at all.

Figures in the first two rows are the PHCP Pros example, not a measurement of any particular house. Your boiler’s own manual may set a higher minimum: Lochinvar’s Knight manual says the boiler is designed for a system of not less than 12 psi. At the other end, the Knight manual lists a 30 psi relief valve setting, and Weil-McLain’s user manual makes its daily check for its water boilers a gauge reading not over 24 psig.

The Cost

How Low Pressure Burns Gas Without Heating the Rooms That Need It

An airlocked upstairs zone can starve the boiler of flow, and Weil-McLain’s troubleshooting table lists insufficient water flow through the boiler as a cause of rapid cycling: the boiler reaches its limit quickly, shuts off and starts again, while the rooms that called for heat still do not warm. The burner is firing, but the heat is not reaching the rooms that asked for it. Weil-McLain’s John Kopf, writing in ACHR News about commercial boiler selection, notes that the longer a boiler runs without cycling, the higher its seasonal efficiency.

The fuel costs more than it did. Indiana’s average residential natural gas price was $11.49 per thousand cubic feet in 2025, up from $9.50 in 2024 and back to about where it sat in 2022 and 2023, according to the U.S. Energy Information Administration. A system that keeps losing pressure adds a second cost: if the fill valve keeps topping it up, fresh water keeps coming in, and Weil-McLain warns that mineral buildup from continual make-up water reduces heat transfer and overheats the metal.

Low pressure is not the same as no water. According to McDonnell & Miller, a low-water cutoff is the only device that can tell whether water is present, and it shuts the burner off before the boiler dry-fires. Weil-McLain’s EG boiler manual says one is required when a boiler is installed above the level of the radiation, or by certain state or local codes or insurance companies, and its user manual tells owners to test the low-water cutoff periodically during the heating season. On a steam boiler it works alongside the gauge glass that shows the water level. If a boiler has run low and is still hot, do not add water to it. Weil-McLain’s manual says it plainly: “Do not add cold water to a hot boiler. Thermal shock can cause the heat exchanger to crack.”

Evaluating a Call

How to Evaluate a Cold-Upstairs Boiler Call

A cold second floor is not by itself a reason to replace a boiler. These questions separate a diagnosis from a guess:

• What does the gauge read cold, and later in the day? On a typical two-story home with the boiler in the basement, roughly 12 psi cold; Weil-McLain’s daily check for its water boilers is not over 24 psig.
• Are the upstairs radiators or baseboard cold at the top? That pattern points toward air. Bleeding a system that is below pressure can pull more air in, and the water can scald, so leave the bleeders to the technician.
• Does the pressure drop between checks, or does the fill valve keep running? Either one means water is leaving the system somewhere, and the leak should be found.
• Does your boiler have a low-water cutoff, and when was it last tested? It is the one safety control that knows whether water is there.
• If a new boiler is recommended for a cold second floor, what did the pressure and flow checks show? If nobody looked, ask for those checks before you decide.

At Dye, every repair proposal is clearly communicated before any work begins, and we can email your estimate.

Dye's Approach

Dye’s Approach

Dye Plumbing & Heating Service Co. has repaired boilers in LaPorte since 1939. Our published boiler diagnostic verifies water pressure and water level, checks expansion tank pressure and condition, tests circulator pumps for proper operation and flow, checks zone valves, and examines piping for leaks, air pockets or blockages. On older steam systems we service the low-water cutoff and the sight glass; steam boilers require specialized knowledge that we’ve developed over decades. We install Lochinvar and repair all major boiler brands. Our plumbing team includes three Indiana Plumbing Contractors, the top license tier in the state. We hold Indiana Plumbing Contractor License PC#10500518, we are Google Guaranteed, our technicians are NATE certified, and we hold 4.8 stars across 440+ Google reviews.