Written October 2026, with Weil-McLain’s and Navien’s own boiler manuals read the same week, and our price book.
Most boiler repairs are one part, not a new boiler. On a hot water boiler that’s usually a stuck circulator pump, a zone valve that won’t open, a waterlogged expansion tank, a dirty flame sensor or air in the pipes. Before you call anyone, check four things: the thermostat, the boiler’s power switch, the pressure gauge, and one press of the reset button (how, below). If the heat still won’t come back, a $99 diagnostic visit anywhere in Northern Virginia finds the part, and you get the repair priced in writing before any work starts. Book it on our boiler repair and replacement page. Wondering if it’s time for a new one? The boiler price estimator shows the range for your house in a few questions.
Smell gas, or a carbon monoxide alarm is going off? Skip the checks: get everyone out, then call 911 and the gas company from outside. No heat in freezing weather is an emergency too, and we run 24/7 emergency service at (703) 997-9757. Typically the same day or the next day, and we’ll tell you honestly when we can get there.
What to check before you call: four things, five minutes
1. The thermostat. Set to heat, a few degrees above the room, fresh batteries if it takes them. A house with zones has a thermostat for each one, so check the one in the cold rooms.
2. The boiler’s switch and the breaker. A boiler has its own on and off switch, usually on the wall near it or at the top of the basement stairs. It looks like a light switch, and it gets flipped by accident.
3. The pressure gauge. Most home hot water boilers are filled to about 12 psi cold, a little more in a tall house, and should stay under about 24 psi hot. The relief valve opens at 30. Near zero means the system has lost water; climbing toward 30 means the expansion tank or the fill valve. Either one is a call.
4. The reset, once. If the boiler shows a lockout, press reset one time. If it fires and runs, book a look anyway, because a lockout has a cause. If it locks out again, leave it off and call: a boiler that keeps locking out is telling you something a reset won’t fix.
On a condensing boiler or a Navien combi, also look at where its white plastic vent pipes leave the house. Snow or leaves over them will shut it down; Navien calls that code E110, exhaust blockage.
Boiler repair: the common problems, and what each one means
Everything here is about hot water boilers on natural gas or propane, the kind that heats radiators or baseboard and has a pressure gauge reading in psi: the old cast iron boilers on the chimney, and the wall-hung condensing boilers and Navien combis that make the hot water too. If yours is a steam boiler (a glass tube on the side showing a water level), burns oil, heats through tubing in the floor, or the trouble is an indirect water heater tank, we don’t work on those, and we’ll tell you so on the phone rather than send someone out.
| What you notice | What it usually is |
|---|---|
| Boiler running, radiators cold | The circulator pump, a zone valve, or air in the loop |
| One radiator cold at the top | Trapped air: bleed it |
| Gauge under about 12 psi cold | Water leaving: a leak, or a relief valve that’s been dripping |
| Gauge near 30 hot, relief valve dripping | A waterlogged expansion tank, or a fill valve that won’t shut off |
| Won’t fire, or locks out | Ignition, the flame sensor, the gas supply, low water or a blocked vent |
| Rumbling or popping like a kettle | Kettling: deposits in the heat exchanger, or too little flow |
| Banging in the pipes | Air, low water, or a pump pushing against a closing valve |
| Water on the floor | The relief valve, a fitting or pump seal, a condensate line, or the boiler itself |
| On and off every few minutes | A boiler too big for the house, or a sensor reading wrong |
No heat, or the radiators stay cold: the water isn’t moving
When the boiler fires and the house stays cold, the hot water isn’t reaching the radiators. Three things cause most of it.
The circulator pump. The small motor on the piping by the boiler that pushes hot water around the loop. When it seizes, the boiler gets hot and the radiators don’t. It’s a repair, not a new boiler.
A zone valve. A house with more than one thermostat usually has a zone valve for each: a small motor head on the pipe that opens when its thermostat calls. One zone cold while the others heat points straight at that valve or its thermostat.
Air in the loop. Air collects at the high points. A radiator warm at the bottom and cold at the top has air in it, and Weil-McLain’s troubleshooting chart gives the fix for radiators that don’t heat or are noisy: bleed the air, and fill back to the right pressure.
To bleed one, let it cool, hold a cup under the bleed valve at the top corner, and open it a quarter turn with a radiator key until the hiss turns to water. Close it, then check the boiler’s gauge, because bleeding drops the pressure. Below about 12 psi, call us to top it up rather than guessing at the fill valve. A radiator that needs bleeding every week has air getting in, and that’s the real repair.
Boiler pressure too low, too high, or the relief valve dripping
A hot water boiler is a closed loop, filled once and meant to stay full. Weil-McLain’s CGi manual says “Typical cold water fill pressure for a residential system is 12 psi,” its user manual says the gauge shouldn’t read past 24 psi, and the relief valve it ships is set at 30. Navien’s NCB-H manuals land in the same place: at least 12 psi cold, and a 30 psi relief valve.
Too low means water is leaving: a slow leak at a fitting or radiator valve, a pump seal, or a relief valve that’s been dripping. Topping it up isn’t the fix, because fresh water brings minerals in with it. Navien: “Continual fresh makeup water will reduce boiler life.” Weil-McLain: makeup water “can cause mineral deposits which, in turn, can cause boiler section failure.” Find the leak before the low water safety shuts the heat off on a cold night.
Too high, or a dripping relief valve, is usually the expansion tank. Water expands as it heats, and the tank gives it room with a cushion of air behind a rubber diaphragm, charged to about 12 psi on a house. When the diaphragm fails, the tank fills with water, and every heating cycle pushes the pressure up until the relief valve lets some out. Weil-McLain’s chart names a flooded expansion tank as the cause of frequent water through the relief valve. The other usual cause is a fill valve that won’t shut off.
Never cap or plug a dripping relief valve. Navien’s manual: “A dripping or leaking pressure relief valve must be replaced. Do not plug or remove the valve.” It’s the part that keeps the boiler from going over pressure.
It won’t fire, or it keeps locking out
A boiler that won’t light is usually its safeties doing their job. Before the burner fires, the control checks for water and a clear vent, and once it lights, a flame sensor has to see the flame. Fail one of those a few times in a row and it locks out.
The usual parts: an igniter or pilot that won’t light, a flame sensor (Navien calls it the flame rod) too coated to read the flame, a gas valve, a blocked vent, or a low water cutoff that tripped because the pressure dropped. Navien’s yearly service list includes “Check ignition and flame rod (clean and reposition).” When you call, tell us whether it never lights or lights and then goes out. Those point at different parts.
A condensing boiler, the wall-hung kind that vents out the side of the house in plastic pipe, pulls so much heat from its exhaust that the water vapor in it condenses. That water drains out through a trap, and it’s acidic: Navien’s installation manual puts it at a pH of 3 to 5. The same manual warns not to let the line “freeze or become obstructed or condensate can flow from the drain,” which is how a clogged line becomes water on the floor. Cleaning the trap is the first item on Navien’s yearly service list.
Before you call about a combi: Navien’s troubleshooting says “When the unit is heating for DHW, the heating side does not work.” A combi pauses the house heat while someone’s in the shower. That’s normal.
The common Navien codes, from Navien’s chart for the NCB-H:
| Code | What Navien calls it | What to do |
|---|---|---|
| E003 | Ignition failure | Make sure the gas valve is open (Navien’s first step), and on propane, the tank isn’t empty. Then call |
| E012 | Flame loss | Call |
| E016 | Heat exchanger overheat | Navien says off for 30 minutes, then restart. The heat exchanger flush it calls for is ours |
| E030 | Exhaust overheat | Leave it off and call |
| E110 | Exhaust blockage | Clear the vent pipes outside. Call if it comes back |
| E352 | High water pressure | Usually the expansion tank or fill valve. Call |
| E777 | Low water cutoff activated | The system is low on water. Call |
Write the code down before you reset anything. It saves time at the boiler.
Kettling, banging and gurgling: what each noise means
Kettling is the rumble or popping of a kettle about to boil. It’s water flashing to steam against the hottest metal, because deposits inside the heat exchanger, or too little flow, keep the water from carrying the heat away. Weil-McLain’s chart traces popping in a boiler to “mineral deposits in sections due to constant use of makeup water,” which usually means a leak that’s been topped up for years. Fix the leak, then clean the deposits out. Weil-McLain is honest that it doesn’t always work: “In some cases, deposits will be too heavy to remove with de-liming procedures.” That’s when kettling means a new boiler.
Banging in the pipes is usually air, low water, or a pump pushing water against a valve as it snaps shut. A tick as the heat comes on is just copper warming against the framing. Gurgling is air moving through the pipes: bleed the radiators, and if it’s back in a few days, something is letting air in.
Boiler leaking water: where it starts decides it
Dry the floor and watch where the water shows up first. From the relief valve’s pipe: pressure, almost always the expansion tank or the fill valve. From a fitting, a valve or the pump: a joint or a seal, both repairs. From a small plastic line under a condensing boiler: the condensate drain, usually a cleaning. From the boiler’s own cast iron sections or heat exchanger: that’s the leak that ends a boiler.
Water on the floor now? Turn the boiler off at its switch, put a pan down and call. Don’t keep adding water, and skip the stop-leak in a bottle: Weil-McLain’s chart says “Do not use petroleum-base stop-leak compounds.”
What you can safely do yourself, and what needs a technician
Yours: the thermostat, the boiler’s switch and breaker, reading the gauge, one reset, bleeding a radiator, clearing snow off a condensing boiler’s vent pipes, and writing down any code.
Ours: adding water at the fill valve (unless someone has shown you how on your own boiler), the relief valve, the expansion tank, the pump and the zone valves, anything with the burner, gas valve, igniter, flame sensor or vent connector, and any code Navien’s chart answers with “contact technical support.” Weil-McLain’s user manual draws the line in the same place: installation and service “must be performed by a qualified installer or service technician.”
Gas smell or a carbon monoxide alarm: get out first
If you smell gas, don’t flip any switch, don’t use your phone inside, and don’t go back to look at the boiler. Get everyone out, then call 911 and the gas company from outside. A carbon monoxide alarm going off means the same thing. Once the fire department clears the house, call us and we’ll find out why it happened. The first ten minutes are in carbon monoxide alarm going off.
No CO alarm in the house? Put one in. Weil-McLain requires its installers to confirm “at least one carbon monoxide alarm is installed in the living space” before a new boiler runs. It’s a good rule for an old boiler too.
Repair or replace: when an old boiler is still worth fixing
Usually it’s worth fixing. A sound cast iron boiler can take new parts for a long time, and age alone isn’t a reason to replace one that heats. Four things change the answer:
- The boiler itself leaks. A cracked cast iron section or a leaking heat exchanger is the end of it.
- Kettling a cleaning won’t fix. Deposits too heavy to come out mean the heat exchanger is done.
- A big repair on a boiler past 20 years old. Put the repair price next to the replacement price before you choose. We’ll write both down.
- The part is hard to get. On an older boiler the question is sometimes whether the part is still made. If it’s on the van, it’s fixed that visit; if not, we order it and book the return, and we’ll say so if it can’t be found.
Efficiency is a reason to choose which boiler goes in next, not usually a reason to pull out one that works. And the federal tax credit is gone: the IRS says it covered improvements made through December 31, 2025.
If it is time, here’s what a new boiler has come to from us, installed:
| New boiler | Installed | Monthly, from |
|---|---|---|
| Cast iron boiler on the chimney, like for like | $9,900 to $13,690 | $165/mo at 0% APR for 60 months |
| High-efficiency condensing boiler, or a combi that makes the hot water too | $12,782 to $16,500 | $213/mo at 0% APR for 60 months |
Monthly figures: 60mo @ 0% APR on each starting price, the whole price financed, on approved credit. Longer plans lower the payment and cost more in total. The lender sets the final terms.
Those ranges are the boilers we’ve actually replaced on current pricing, and yours gets written down at the house first. Where it lands depends on how it vents (a chimney that needs a liner on a cast iron swap, or a new hole in the wall for plastic pipe), how much piping gets rebuilt, and whether it makes the hot water too. We install Navien, Weil-McLain and Force (the ProSelect line Ferguson carries). The long read is what a boiler replacement costs in Northern Virginia, and holding another company’s quote, we’ll give you a free second opinion on it.
The boiler repairs a yearly tune-up heads off
Both makers ask for it. Weil-McLain: “The boiler must be inspected and started at the beginning of the heating season every year by a qualified service technician.” Navien wants its boilers “inspected annually, preferably at the start of the heating season.” That visit checks most of what’s above: pressure, the expansion tank, the relief valve, the flame and its sensor, the venting, the pump and valves, and on a condensing boiler, the condensate trap.
Our boiler tune-up is $99 a system, the same as a furnace tune-up. If it finds a repair, you get the price in writing first, and you decide. Current deals are on our offers page, and the visit, item by item, is in boiler service before winter.
Boiler repair after hours, and what counts as an emergency
No heat in freezing weather is an emergency, and so is a cold night with someone very young, elderly or sick in the house. We run 24/7 emergency service. Typically the same day or the next day, and we’ll tell you honestly when we can get there. Weil-McLain’s manual is blunt about why it can’t wait: a boiler failure in cold weather “could result in frozen plumbing and water damage in a matter of hours.”
If another company told you next week, call us and ask. If we can’t do better, we’ll say so on the phone. How that works from Chantilly to Old Town is in emergency boiler repair in Alexandria.
Who comes out, and the boiler pages by town
A hot water boiler is half heating system and half plumbing, and we run separate heating and plumbing teams, so each half gets a tech who does that trade every day. The $99 diagnostic covers the whole system, not just the noisy part, and ends with the repair priced in writing. You approve it or you don’t.
These towns have their own boiler pages, with what the houses there are like and the same prices: McLean, Arlington, Alexandria, Falls Church, Vienna, Annandale and Fairfax, and every other town is on our boilers page. Our heating posts for McLean and Falls Church cover the boiler houses there, and a gas furnace or heat pump is in heating repair.
Boiler repair questions, answered straight
How much does boiler repair cost?
From us, a $99 diagnostic, then the repair priced in writing at the boiler before any work. Our price book doesn’t list boiler part prices, so nobody here will guess at one over the phone. If the boiler itself is done, our replacements have run $9,900 to $16,500 installed. From about $165 a month at 0% APR for 60 months, the whole price financed, on approved credit.
Do you do boiler repair near me?
Anywhere in Northern Virginia, out of Chantilly and Ashburn, on any make of hot water boiler, including ones we didn’t install. Typically the same day or the next day, and we’ll tell you honestly when we can get there.
Why is my boiler not heating?
Running with cold radiators: the water isn’t moving, usually the circulator pump, a zone valve or air. Not running at all: check the thermostat, the switch and the gauge, then press reset once. If it locks out again, call.
Why is my boiler pressure too high?
Usually a waterlogged expansion tank or a fill valve that won’t shut off. Weil-McLain says the gauge shouldn’t read past 24 psi, and the relief valve opens at 30. Climbing toward 30 or dripping: call, and never cap the valve.
Why is my boiler making banging noises?
Usually air, low water, or a pump pushing against a closing valve. A rumble like a kettle is kettling, which Weil-McLain traces to mineral deposits from years of topping up a leak.
Is it worth repairing an old boiler?
Usually, when the boiler is sound and the problem is a part. Replace it when the sections or heat exchanger leak, when kettling won’t clean out, or when a big repair lands on a boiler past 20 years old.
Why is my boiler leaking water?
Check where it starts: the relief valve’s pipe means pressure, a fitting or the pump means a seal, a plastic line under a condensing boiler means the condensate drain. Water from the boiler’s own sections means it’s done.
On the NCB-H, E003 is ignition failure, E012 flame loss, E016 heat exchanger overheat, E110 exhaust blockage, E352 high water pressure and E777 low water. Write it down before you reset.
Get your boiler looked at
Call (703) 997-9757 or book online. Tell us what the gauge reads, whether the boiler fires, any code on the display, and its age if you know it. Prices are on our boilers page, and the estimator gives your house its own range.
SwiftPro Heating, Cooling & Plumbing repairs, tunes up and replaces hot water boilers, gas and propane, across Northern Virginia from Chantilly and Ashburn, and installs Navien, Weil-McLain and Force. Family owned, BBB Accredited with an A rating, 24/7 emergency service, Virginia Class A contractor license 2705192276, and rated 5.0 stars across 1,132 reviews on Google, Angi, Yelp, the BBB and Facebook. Read the reviews.
