Boiler Repair & Installation in Seattle & Eastside
Repair, Replacement and Installation
Most people reach this page for one of three reasons: the boiler has stopped working, it is limping along and they are deciding whether to fix it, or it has finally gone and they need it replaced before the weather turns. This page covers all three, plus what a visit actually involves and how we work on hydronic systems across Seattle and the Eastside.
Boilers sit at the crossover of heating and plumbing. A technician who only knows forced air will struggle with them. We hold Washington construction, electrical and plumbing licences, which is what that crossover actually requires.
Repair
No heat, no hot water, pressure loss, noise, a lockout that keeps returning. We diagnose before we quote parts.
Replacement
When repair stops making financial sense. We size the new unit to the house rather than matching the old nameplate.
Maintenance
An annual service that catches the faults that otherwise become a January callout.
Boiler Repair
Boilers are complex, and the same symptom can have several causes. A drop in pressure might be an expansion vessel that has lost its charge, a leaking fitting under a floor, or a discharging pressure relief valve — three very different jobs. Diagnosing properly matters more on a boiler than on almost anything else we work on, because guessing at parts gets expensive quickly.
What we get called out for most
| Symptom | What it usually turns out to be |
|---|---|
| No heat, no hot water | Ignition or flame sensing, a failed circulator, or a control fault. Often a lockout the boiler is reporting if you know where to look. |
| Pressure keeps dropping | A leak somewhere in the loop, a spent expansion vessel, or a relief valve passing. Topping it up repeatedly hides the fault rather than fixing it. |
| Banging or kettling | Scale or sludge in the heat exchanger, or poor circulation. Usually a system water problem rather than a boiler problem. |
| Some radiators cold | Air, a seized zone valve, or a balancing issue. The boiler is often working fine. |
| Yellow flame or soot | Incomplete combustion. This one is not a wait-and-see — it means carbon monoxide risk and needs looking at straight away. |
WORTH KNOWING
Yellow flames on a gas burner or black soot on an oil boiler mean fuel is not burning properly, and that produces carbon monoxide. If you see either, stop using the system and get a working CO detector in the house. This is the one boiler symptom that is a safety matter rather than a comfort one.
Repair or Replace?
The honest answer depends on age, what has failed, and what the repair costs against a replacement. We will give you both numbers rather than quietly quoting the repair.
Signs that point toward replacement rather than another fix:
| Sign | Why it matters |
|---|---|
| Age | Well-maintained boilers commonly run 15 years and often far longer — we still service cast iron units decades old. But past a certain point, parts availability and efficiency both work against you. |
| Rising energy use | Bills climbing with no change in habits usually means the system is working harder for the same heat. |
| Repeat repairs | One repair is a repair. Three in two winters is a replacement you are paying for in instalments. |
| Combustion problems | Discoloured flame or soot points at something fundamental rather than a component. |
Boiler Installation and Replacement
A replacement is a design job, not a swap. The right output depends on the heat loss of the house and what the system is asked to do — radiators, in-floor loops, domestic hot water, or some combination. Fitting the same size as the old one because it is what was there is how houses end up with an oversized boiler that short cycles and costs more to run than it should.
We work with condensing gas boilers, including Viessmann, and with Uponor for in-floor distribution. Where a high-efficiency condensing unit will genuinely deliver on its rating, we will say so; where the existing emitters would need running too hot for it to condense, we will tell you that too, because a condensing boiler that never condenses is an expensive way to buy the same efficiency you already had.
What a replacement usually involves
A heat loss calculation, a look at the existing pipework and emitters, gas supply and flue routing, and a decision about controls. Where the old system has no zoning or the controls are original to the boiler, that is often where the comfort gain actually comes from rather than the appliance itself.
Hydronics, Radiant and Why Boilers Are Our Thing
Most heating companies in this region are forced-air shops. Furnaces and heat pumps are what they install, and boilers are what they refer out. We are the other way round: hydronic heating is a core part of what NW Mechanical does, alongside radiant and in-floor systems and water heating.
That matters when something is wrong with a system rather than an appliance. Zoning, circulator sizing, mixing valves, buffer tanks and system water quality are all boiler-adjacent problems that a forced-air technician will not usually have spent much time on. It also matters on older Seattle homes, where a hydronic system may have been extended piecemeal over fifty years and needs someone willing to work out what is actually connected to what.
What We See Across Seattle and the Eastside
| Where | What we typically find |
|---|---|
| Older Seattle homes | Original cast iron boilers and radiator systems, often still sound, sometimes extended without much thought for balance. Replacement here is as much about the distribution as the boiler. |
| Bellevue and Kirkland | Larger homes with multiple zones and in-floor loops, where the complaint is usually one zone rather than the whole house. |
| Woodinville and the north Eastside | A mix, including propane and oil on properties off the gas main, which changes the replacement options considerably. |
| Newer construction | Condensing units with in-floor distribution, where most faults trace back to controls or commissioning rather than the appliance. |
Boiler Maintenance
Boilers reward annual servicing more than most equipment, because the faults that strand you in January are usually visible in September. A yearly visit covers combustion, pressure and expansion, the circulator, controls and safety devices, and system water condition.
Our Service Partner Plan schedules it so you do not have to remember, and puts you ahead of the queue when the first cold snap fills the calendar.
Frequently Asked Questions
How long should a boiler last?
Fifteen years is a reasonable expectation with annual servicing, and plenty run far longer — older cast iron units in Seattle homes routinely pass forty. Age alone is not a reason to replace. Repeat failures, rising running costs and parts availability are.
My pressure keeps dropping. Can I just keep topping it up?
You can, but it is a symptom rather than a fix. Persistent pressure loss means water is leaving the system somewhere, or the expansion vessel is no longer doing its job. Repeated topping up also introduces fresh oxygenated water, which accelerates corrosion.
Do you work on boilers you did not install?
Yes. Most of the boilers we service were installed by somebody else, often decades ago.
Is a condensing boiler always more efficient?
Only if the system lets it condense. That requires return water temperatures low enough for the flue gases to give up their latent heat, which depends on your radiators or in-floor loops, not just the boiler. On some retrofits the emitters need attention for the rated efficiency to be real.
Can you handle both the heating and the plumbing side?
Yes, and on boilers that matters. We hold Washington construction, electrical and plumbing licences, which is what a hydronic system usually touches.
How quickly can you come out if we have no heat?
Call us and we will tell you honestly where you are in the queue. Emergency heating repair covers same-day response across Seattle and the Eastside.
Licensed, Bonded and Insured
Family-owned, based in Woodinville, serving Seattle and the Eastside.
WA CONSTRUCTION
NORTHM*799CA
WA ELECTRICAL
NORTHM*794CF
WA PLUMBING
NORTHM*760NG
UBI
604 682 203
Boiler Playing Up, or Finally Done?
Tell us what it is doing and we will tell you whether it is worth fixing.
Some of the most common boiler problems we handle include:
If your boiler has reached the end of its lifespan, we can help with the replacement as well. Boilers today are more energy-efficient and you can rest easy knowing our team can install your new system with the utmost care and professionalism. In addition to boiler services in Seattle, we repair and replace other plumbing-based systems such as water heaters and radiant heat.
Your Choice for Home Comfort Solutions
Boiler Repair
Water Heaters
Radiant Heat
Related Home Comfort Services We Provide
Boilers aren't the only home comfort systems we specialize in. Whether you need service on an existing unit or you're planning an upgrade, our team provides the same detailed, reliable workmanship on every system we install and maintain for homes throughout Seattle and the Greater Eastside.
We Offer Services For:
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At NW Mechanical, your comfort is our top concern. Allow us to handle all your boiler needs. We are prompt, reliable, and friendly. Our team also offers estimates and stands behind all our work with a satisfaction guarantee.
Trusted Since 1977
Homeowners across Seattle and the Greater Eastside trust NW Mechanical for their boilers, water heaters, heating and air conditioning, heat pumps, and whole-home comfort. Here's what our customers have to say.
Greater Eastside & Seattle Heating, Air & Home Comfort
For fast, reliable heating, cooling and HVAC service across Seattle and the Greater Eastside, contact NW Mechanical, where your comfort comes first. Our highly trained technicians handle everything—from simple tune-ups and repairs to full system replacements—for any brand or model.
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