Is your boiler hot water or steam?
Boiler systems come in two kinds, and they fail in different ways, so it helps to know which one you have before you call. Look at the boiler and at any radiator:
| Clue | Hot-water system | Steam system |
|---|---|---|
| On the boiler | A pressure and temperature gauge, with a circulator pump nearby | A glass sight tube showing the water level, and a pressure control |
| At the radiators | A small bleed valve near the top, opened with a radiator key | On one-pipe systems, an air vent on the side that hisses as steam arrives |
| What else it can heat | Fin-tube baseboard, radiant floors and an indirect water heater | Radiators and convectors |
| Typical noises | Gurgling from trapped air, kettling from scale or weak flow | Banging from trapped water, spitting vents |
| Replacement options | Condensing, cast-iron or combi boilers | A steam boiler, since condensing boilers are hot-water only |
How does a boiler repair visit work?
- Call or send the form. The number is 612-429-3465. We're open 7 days a week, 7am–9pm, and a house with no heat goes first.
- We start with the basics. Thermostat, power, the burner's lockout status, and the pressure gauge or sight glass.
- We work through the system. On hot water: burner, circulators, zone valves, expansion tank, air removal and the relief valve. On steam: water level, the low-water cutoff, the pressure control, the main vents and the piping near the boiler.
- You get a written price first. Nothing gets replaced until you approve a flat-rate price, and the $79 trip charge is waived when you do.
- We repair it and run it. The boiler runs through a cycle while we check venting and carbon monoxide around it and confirm every zone heats. Completed repairs carry a written 1-year parts-and-labor warranty.
What do common boiler problems mean?
| What you notice | Likely cause | What we do |
|---|---|---|
| Radiators cold at the top, or an upper floor cold | Air trapped in a hot-water loop | Bleed the radiators, check the air separator and the fill pressure |
| Relief valve dripping or dumping water | A waterlogged or failed expansion tank, a fill valve letting in too much water, or a worn relief valve | Test the tank, fill valve and relief valve and replace what failed; the relief valve never gets capped |
| Rumbling or tea-kettle sound | Scale or sludge in the heat exchanger, or weak flow from a failing circulator or stuck zone valve | Check flow and circulators, then flush or treat the system |
| One zone stays cold | A failed zone valve, zone circulator or thermostat | Test each zone's controls and replace the failed part |
| Steam pipes bang | Water trapped where a pipe lost its pitch, a water level set too high, or too much pressure | Check the pitch, water level and pressure control |
| Far radiators on a steam system stay cold | Clogged or stuck main vents or radiator vents | Test and replace the vents, then check the pressure setting |
| Boiler won't fire | A tripped low-water cutoff, failed ignition or flame sensor, or a control fault | Trace the burner's sequence and test the failed part |
| Water under the boiler | A leaking valve, pump seal or fitting, or a leaking heat exchanger | Find the source; a leaking heat exchanger usually means replacement |
Our post on boiler banging and kettling noises goes deeper on the sounds and what you can check yourself.
Hot-water and steam systems, part by part
Hot water: radiators, baseboard and radiant floors
A hot-water system is a closed loop. The boiler heats water, a circulator pushes it through the radiators, baseboard or floor tubing, and it comes back cooler to be heated again. Zone valves or separate circulators split the house into zones, each with its own thermostat. Water expands as it heats, and the expansion tank absorbs that growth. When a bladder tank fails or an old steel tank fills with water, pressure spikes every time the boiler fires, and the relief valve, rated at 30 psi on most home boilers, starts to drip. Capping that valve is dangerous. Fix the tank instead.
Radiant floors run much cooler water than radiators, usually through a mixing valve, and they respond slowly, so they don't handle big thermostat setbacks well. Our radiant floor vs baseboard guide compares the two.
Steam: one-pipe and two-pipe
A steam boiler makes steam at very low pressure. It rises to the radiators, gives up its heat, condenses and drains back to the boiler by gravity, so every pipe has to keep its pitch. On a one-pipe system, steam goes up and water comes back down the same pipe; a two-pipe system has a separate return and usually a trap at each radiator. Vents on the mains and on one-pipe radiators let air out so steam can get in. The checks that matter are the water level in the sight glass, a low-water cutoff that gets tested and flushed as the manufacturer directs, and a pressure control set low. Turning the pressure up doesn't heat the far radiators faster. It burns more fuel and makes the system louder.
Boiler heat in Minnesota houses
Drive through the older parts of Saint Paul and Minneapolis and many of the four-squares, bungalows, duplexes and Victorians built before World War II still heat with a boiler. Some of those boilers are decades old, and others were replaced once already while the cast-iron radiators and piping stayed. The same pattern shows up in the historic parts of river towns like Stillwater, Hastings and Red Wing. Newer boiler systems are usually radiant floors: tubing in a basement slab, a heated garage or shop floor, or a custom home that went hydronic from the start. Lake homes and farmhouses past the gas lines often run their boilers on propane.
A boiler that quits on a sub-zero night can let pipes in exterior walls, porches and unheated rooms freeze, so a no-heat boiler call goes to the front of the line. Old piping brings one more caution: the white or gray wrap on older steam and hot-water pipes can contain asbestos, so it shouldn't be cut or disturbed until it's tested.
CenterPoint Energy supplies gas in Minneapolis, and Xcel Energy supplies it in Saint Paul. CenterPoint's heating rebates cover high-efficiency boilers and let you use the dealer of your choice. Xcel Energy lists gas boiler rebates too, so ask Xcel whether yours needs a registered contractor before you buy. The federal 25C tax credit, which covered boilers, ended for equipment placed in service after December 31, 2025. Our local pages cover boiler service in Saint Paul and Minneapolis.
Any fuel-burning boiler can produce carbon monoxide if it vents poorly. Minnesota law requires working CO alarms within 10 feet of every sleeping room, and our CO alarm placement guide shows where they go.
Should you repair the boiler, replace it or add cooling?
A cast-iron boiler with a sound heat exchanger can run a long time with good care. We usually recommend replacement when the heat exchanger leaks, when parts for the burner or controls are no longer made, or when repair bills keep stacking up on an old boiler.
Sizing starts with the house, not the old nameplate: a Manual J heat-loss calculation for a hot-water system, and a count of the connected radiation for steam, since a steam boiler has to match its radiators. A hot-water system can usually take a modulating condensing boiler. It saves the most when the water coming back to it is cool, which radiant floors deliver all season and radiators deliver on milder days, and an outdoor reset control helps by lowering the water temperature as the weather warms. Steam has to stay steam. A combi boiler, like the wall-hung units Navien makes, handles heat and hot water in one appliance and suits smaller homes, while a boiler with an indirect water tank suits houses with several bathrooms in use at once. If a new boiler vents through PVC, the water heater left in the old chimney may need a liner. We service Weil-McLain, Navien and the other major boiler makers.
Boiler homes don't have ductwork for air conditioning. Ductless mini-splits are the usual answer in older houses where cutting in ducts would mean tearing into plaster, and a high-velocity small-duct system is another option.
How much does boiler work cost?
A boiler service call is a $79 trip charge, waived when you approve the repair. You get a written, flat-rate price before we start, and completed repairs carry a 1-year parts-and-labor warranty. Boiler maintenance visits fall within our $129–$349 maintenance range, with the price for your equipment confirmed when you book. Pricing is the same in every town we serve, with nothing added for distance.
We don't publish a boiler replacement range, because steam versus hot water, the amount of radiation and the venting change the job too much. We look first, then quote in writing. For national context, cost guides such as HomeGuide put a typical gas boiler replacement at $4,000–$9,000 and a high-efficiency boiler at $4,000–$10,000, with standard-efficiency boilers starting around $2,200. Installs carry a 2-year labor warranty on top of the manufacturer's parts warranty, and financing is available.
Our post on boilers vs furnaces in Saint Paul homes compares replacement costs for both. The pricing page lists every published price, and our cost pages for Saint Paul and Minneapolis cover HVAC costs in each city. Call 612-429-3465 to book a boiler visit.
What's included with boilers & radiant heat?
- Boiler, burner and control diagnosis for hot-water and steam systems
- Circulator, zone valve and expansion tank checks
- System pressure, relief valve and low-water cutoff testing
- Air purging and radiator bleeding on hot-water systems
- Venting and carbon monoxide check around the boiler
- Written, flat-rate price before any repair begins
- Written 1-year parts-and-labor warranty on completed repairs
Boilers & Radiant Heat questions
Why is my boiler making a kettling sound?
Kettling is water flashing to steam in spots inside the heat exchanger. Usually scale or sludge has built up on the heating surface, or water isn't flowing through the boiler fast enough. A failing circulator or a zone valve stuck shut can cause it too. It's hard on the heat exchanger, so have it checked instead of waiting to see if the sound goes away.
Why do my steam pipes bang?
Banging, or water hammer, usually means condensate is trapped in a pipe that has lost its pitch, and steam slams into that water. Other causes are a boiler running at too high a pressure, a water level set too high, or a one-pipe radiator valve left half open. Those valves should be fully open or fully closed. Old steam systems are forgiving, but only when the pitch and pressure are right.
Why is my boiler's relief valve dripping?
Usually because the system pressure climbs too high when the boiler fires. Most often the expansion tank has lost its air charge or filled with water, and a leaking fill valve can push the pressure up too. The relief valve is doing its job, so never cap or plug it. Have the tank and fill valve checked, and replace the relief valve if it keeps weeping after the pressure is fixed.
How do I bleed my radiators?
On a hot-water system, turn the heat down and let the radiators cool. Hold a rag under the small bleed valve near the top of each radiator, open it with a radiator key, and close it once water comes out in a steady stream. Check the boiler's pressure gauge afterward, since bleeding lets water out. Steam radiators work differently and use automatic air vents instead.
Should I replace my old cast-iron boiler with a furnace?
Usually not. If the radiators and piping are sound, a new boiler keeps the quiet, even heat you have and avoids cutting ductwork into plaster walls. Switching makes sense mainly when you're already opening walls in a remodel or the piping itself is failing. The one thing a boiler can't do is carry air conditioning, and ductless mini-splits usually cover that.
What is a combi boiler?
A combi boiler heats the house and makes domestic hot water on demand from one wall-hung unit, so the separate water heater goes away. It suits smaller homes and condos with modest hot-water use. In a house with several bathrooms in use at once, a boiler with an indirect water tank is often the better fit. Most combi boilers are condensing units that vent through PVC and need a condensate drain.
What does a new boiler cost?
National cost guides such as HomeGuide put a typical gas boiler replacement at $4,000–$9,000. We don't publish our own range, because steam or hot water, the amount of radiation, the venting, and extras like an indirect water heater or new zones change the job too much. We look at the system first, then give you a written, flat-rate quote. Installs carry a 2-year labor warranty on top of the manufacturer's parts warranty.
Can I get air conditioning in a house with radiators?
Yes, without touching the radiators. Ductless mini-splits are the usual answer: an outdoor unit connected by a small line set to wall-mounted heads in the rooms that need cooling. High-velocity small-duct systems are another option, running flexible tubing through closets and attic space. Either way the boiler keeps heating the house, and a cold-climate mini-split can carry some of the heating in fall and spring too.
Sources
- HomeGuide cost guides (2026 editions) homeguide.com