Westford Navien Combi Boiler Kept Running: What We Checked

A homeowner in Westford called us about a Navien combi boiler that kept running after another company's rework. Two mechanical rooms had flooded, and the pressure gauges didn't agree. We found an active leak at a fitting added during that rework, and stopping it came first. We didn't confirm on that visit that the leak explained the other symptoms, so they needed their own checks.

Safety first

If you smell gas or a carbon monoxide alarm sounds, leave the house and call 911 from outside. Don't operate switches, phones, appliances or valves inside. Stay out until the fire department or gas utility clears the property. For escaping hot water or water near electrical equipment, keep clear. Use the boiler's shutdown instructions only if you can reach the boiler safely from a dry spot, and arrange urgent service. Don't open the cabinet or plug a discharge pipe.

What happened in this Westford home

The homeowner told us the Navien combi boiler, which handles both heat and domestic hot water, was two to three years old and had been working well. Then another company came out with an inspector and recommended a neutralizer and additional brass fittings. After that work, a large discharge of water flooded two mechanical rooms below. The homeowner had to shut the water off by hand, and that month's water bill came to about $800. That history told us where to start looking, but timing alone didn't prove what caused each problem.

When we arrived, the first-floor system was showing an error. At the third-floor unit, one pressure gauge read 11.6 psi and another just over 20, where we expected about 15 psi. The boiler kept running and never seemed to reach its shutoff temperature. From that visit, we can't say whether all of this involved one boiler or more than one. A gauge reading depends on where the gauge sits, its height in the system, whether the pump is running and the water temperature, so these numbers aren't settings to copy.

Tracing the leak

During our checks, the pressure-reducing valve and the air vent both worked. Following the discharge line down to the basement, we found water escaping at an added fitting and marked it for replacement. A relief valve's discharge line is there to carry water away when the valve opens, so water in that line doesn't by itself mean a fitting is bad. Here, the leak at the fitting itself showed the part had failed.

The fitting was part of the other company's rework: they had moved the pressure relief valve from its original position and added brass hardware. Whether the new arrangement is acceptable depends on the boiler's installation instructions and the piping as installed. The relief valve and the air vent do different jobs: the relief valve opens to release water when system pressure gets too high, and the air vent lets trapped air out.

What we recommended for the system water

We found no evidence that the system had ever been properly flushed. That's a reason to check the system water and look for deposits, not proof that cleaning was never done. We recommended circulating a cleaner approved for the boiler, then thoroughly flushing and refilling the system and adding an inhibitor where it suits the boiler and the water chemistry. The product, its concentration and how long it circulates have to follow the boiler's and the cleaner's instructions.

We estimated roughly two hours of cleaner circulation and about half a day of work per unit. Those were planning estimates, not fixed treatment times or a record of finished work. The system also had no magnetic filter. A magnetic filter can catch magnetic iron particles, but it doesn't remove every kind of debris or replace a proper cleaning. The boiler model and the system's condition decide whether a filter belongs in the plan, and which one.

What a sound combi boiler repair covers

A combi boiler repair after rework like this starts with safely stopping the water loss and confirming which part failed. Then the technician checks fill pressure, expansion control, relief protection, air removal and control operation under the model's procedures, and compares gauge readings at known locations and operating conditions. Any cleaning, inhibitor or filtration belongs in a written scope based on those findings. Final operating checks show whether the constant running and the water loss have stopped. We don't have final readings from this home to share, so we can't tell you how it turned out.

Jeneral Plumbing is owner-operated by a Licensed Master Plumber (MA #9628831-PL-M) who is Navien Service Specialist (NSS) certified and factory trained by Navien. Our heating service covers boiler diagnosis, repair and commissioning for the space-heating side. Our water heater service covers the domestic hot water side.

What should I ask a contractor about Navien combi boilers?

Ask about their experience with Navien combi boilers, how they select fill pressure and relief-valve arrangements, and what cleaning or water treatment the model requires. Ask whether a magnetic filter is appropriate and what it captures. A qualified contractor should explain the plan and put the work and operating checks in writing.

Scheduling boiler service in Westford

We're based in Westford, MA, and serve homes within 20 miles across Middlesex & Worcester County, confirming your address, work and availability before booking. Gas appliance work is Massachusetts-only. Every regular-hours visit carries an $80 dispatch fee — the cost of the visit, waived when you hire us for the work. If your boiler runs constantly, pressure readings have changed or your water bill has jumped without explanation, call (978) 392-7789 to discuss an assessment. Work is priced at a flat rate for approval before it begins.