Commercial boiler and hydronic repair

The boiler is only half the heating plant

When a building goes cold, the call usually says "the boiler is out." Sometimes it is. Just as often the boiler is hot and happy and the heat is not leaving the mechanical room: a circulator pump has lost its coupling, a zone valve is stuck shut, air has collected at the top of the loop, or the control that stages the boilers is reading a failed sensor. A hydronic system is a boiler, a set of pumps, a web of piping and valves, an expansion tank and a control strategy, and any one of them can leave people in coats.

So we start at the boiler and walk the loop. Supply and return temperatures, system pressure, pump amps and valve positions tell us early on whether the problem is making heat or moving it.

Boiler and loop faults we find most

What you see	What is usually behind it
Boiler locked out, won't light	A dirty or failed flame sensor, ignition problem, gas pressure issue, a tripped low-water cutoff or a flame safeguard doing its job.
Short cycling	Too little flow through the boiler, an oversized boiler on a mild day, a bad temperature sensor, or staging controls set too tight.
Relief valve dripping or blowing	A waterlogged expansion tank, a failing pressure-reducing valve on the fill line, or system pressure set too high.
Some zones cold, others fine	Air trapped in the piping, a stuck zone or control valve, an unbalanced loop, or a pump that is running but not moving water.
Pump noise or vibration	Cavitation from low suction pressure, worn bearings, a failing coupling on a base-mounted pump, or debris in the impeller.
System keeps losing pressure	A leak somewhere on the loop, a weeping pump seal, or a relief valve that is not reseating. Constant makeup water also brings in fresh oxygen and minerals that attack the boiler.

Low-water cutoffs, high-limit controls and relief valves are safeties. We find out why one tripped before we put the boiler back in service, and we never bypass one to get heat back on.

Circulator pumps, valves and the rest of the loop

Pumps do the hauling in a hydronic system, and they run for months at a time. Small inline circulators fail at the motor or the cartridge. Larger base-mounted pumps wear out mechanical seals, bearings and flexible couplings, and a misaligned coupling will chew through all three. We check pump amps, listen for cavitation, look at the seal for weeping, and read the gauges across the pump to see whether it is doing real work.

Many buildings use the same pumps and piping for chilled water in summer, so a pump problem is a year-round problem. The loop side of our work ties directly into chiller service on buildings that run both. Valves round out the list: zone and control valves, three-way mixing valves, balancing valves, check valves that stick open and let hot water flow backward, and the air separators and vents that keep the loop quiet.

Low-pressure boilers we service

Our boiler work is on low-pressure equipment: the cast iron sectional boilers, steel firetube boilers and modular condensing boilers that heat offices, schools, churches, clinics, apartments over retail and light industrial buildings. That covers the burner, ignition and flame safeguard, the heat exchanger, the controls, and every pump and valve on the loop. High-pressure steam and power boilers are outside the work we do.

We cover boiler calls in Lebanon and Wilson County, in Nashville commercial buildings, and across Gallatin, Murfreesboro, Clarksville and the towns around them.

Fall startup and the heating season

Nashville's normals show about 3,364 heating degree days a year against 1,873 cooling degree days (NOAA 1991–2020 normals). Heating is a real season here, and a boiler that sat cold since April deserves a real startup rather than a flip of the switch on the first cold Monday. A fall startup visit on a boiler maintenance agreement covers:

• Burner and ignition inspected and cleaned, flame signal checked
• Combustion readings taken and compared with last season
• Low-water cutoff, high limit and flame safeguard tested, not assumed
• Relief valve inspected, expansion tank charge and system fill pressure verified
• Circulator pumps started, amps and rotation checked, seals and couplings inspected
• Air vents and separators cleared, zone valves stroked, supply and return temperatures logged

If the heat is out on a cold night, the same phone line handles emergency boiler calls around the clock.

Repair or replace a boiler?

ASHRAE's median service life estimates put steel firetube boilers at about 25 and cast iron boilers at about 35 years, and a well-treated loop helps them get there. We repair boilers until repair is no longer economical, and cast iron sections, burners and controls can often be replaced without replacing the whole boiler. When the heat exchanger is failing or parts are gone for good, we lay out the choices, including splitting one large boiler into smaller modular units, and help you plan an equipment replacement over the summer instead of in January.

Boiler questions