This page covers the gas fault families at Philadelphia scale: ignition, flame sensing, condensate, and the venting decay hiding in old masonry chimneys.
General inquiries: 7 AM–7 PM · Emergency calls: 24/7 · (888) 766-1474
Fuel type varies by property. Check whether the boiler uses gas, oil, propane, or electricity before calling; the fuel source affects the appropriate diagnostic steps.
Philadelphia doesn't just use gas; it is built around it. The stock spans atmospheric workhorses — many converted from coal or oil generations ago — across South Philly and the older Northeast; sealed mid-efficiency units from the great replacement waves of the 80s and 90s; and condensing wall-hungs in newer Northeast blocks and recent swaps. Attached housing adds its own wrinkle: a venting problem in one rowhouse can become the neighbor's CO alarm.
Tell the triage which generation you have — masonry chimney or white PVC venting is the instant visual test — because the fault families barely overlap: ignition and flame on atmospheric, venting and controls on mid-efficiency, condensate and sensors on condensing.
The atmospheric generation's signature failure.
Call for heat, inducer runs, igniter glows or sparks, valve opens, flame proves — and on the city's vast atmospheric stock, the proving step is where age lives. Oxidized flame sensors report no flame despite a healthy burner (the fires-then-quits-then-locks-out loop Philadelphia techs could diagnose in their sleep); cracked hot-surface igniters that never light at all; thermocouples expiring on the oldest standing-pilot units.
Reset once to observe, then stop — repeated resets on old atmospheric equipment risk unburned gas accumulation, and they erase the failure pattern the tech needs. Note where the sequence dies and bring the error code if there is one.
Two generations, two weather problems.
Condensing units (Northeast, recent swaps): January in the teens freezes exterior condensate runs solid. Trap backs up, pressure switch trips, lockout on a perfectly good burner. Failures that happen only on the coldest nights are the tell; interior termination with proper fall is the cure.
Atmospheric units on old masonry (South Philly, older stock): chimneys built for coal, now carrying gas, run cool enough to condense flue gases internally — acid eating mortar from the inside. White exterior blooming, sandy mortar joints, mild-weather lockouts. In rowhouses, get this checked promptly: your flue problem can become the attached neighbor's problem.
No guessing on gas.
Generation first (atmospheric? sealed? condensing?), then combustion analysis — the analyzer goes in the flue on every gas visit, full stop. Supply pressure, ignition components under load, flame signal measured in microamps, condensate path and venting integrity including the chimney's structural state, water side at 12–15 psi cold with expansion tank and auto-fill verified.
CO screening is part of every visit — the test that never gets skipped on fuel-burning equipment, least of all in attached housing where one home's venting affects the next.
Straight answers before you call.
The usual sequence is flame sensor fouling, ignitor wear, or a condensate blockage tripping the safety — in that order of likelihood. Sealed units are chatty: the fault code or the blinking light pattern tells the tech where the sequence stopped. Note exactly what the boiler does before it locks out; that description is half the diagnosis.
Yes — a blocked condensate trap or frozen exterior run will shut the boiler down, and it is one of the most common no-heat calls on condensing units in winter. The trap needs periodic cleaning, and exterior runs need freeze protection. If the unit is faulting on condensate, do not keep resetting it; the blockage is still there.
It depends on whether the chimney was lined for the new unit. Old Philadelphia chimneys are oversized for modern gas exhaust, which causes condensation damage inside the flue and lazy draft that trips safeties. A proper liner sized to the boiler solves both. If your replacement skipped the liner, the chimney has been telling on itself for years.
In the places you do not look: weeping radiator valves behind furniture, baseboard connections inside finished walls, and the expansion tank slowly failing in the corner. The auto-fill valve covers the loss by topping up, so the first sign is often the relief valve dripping. A pressure gauge that will not hold steady cold is the tell — investigate, do not just refill.
It depends on condition, not age alone — some of those old blocks are sound and worth their ignition parts, others are weeping and done. The honest test is frequency: an occasional thermocouple is maintenance, but repeated lockouts plus a damp block mean the boiler is voting. A tech who sees the unit in your basement will give you the straight version.
Related services in the Philadelphia area.
Not the gas side? The general repair page triages across fuels, with special attention to the gas-vs-steam fork that defines Philadelphia diagnosis. Steam owners should see the national steam boiler repair guide; the rare oil holdouts are covered on the oil boiler page. No heat on a freezing night is an emergency call; a finished block leads to the replacement page. Nationally, gas boiler repair and condensing boiler repair go deeper.
Call (888) 766-1474 — note the error code and the venting type, and get connected to a local pro.
