What a technician actually does
air bound system that needs bleeding and repressurizing [S1]
high likelihood moderate $150–$250 installed about 60 min
the radiators never get hot the pipes bang and hammer when the heat comes on
S1 lists bleeding and repressurizing among its minor repairs at $150-250, and S2 describes why it comes up so often in this market: it classes the pre-war Glenside and Wyncote systems as steam or gravity hot water, and it says boiler pressure problems there are usually a failed pressure reducing valve or air binding in the system. Air trapped in a hot-water loop stops circulation at the radiator with the boiler firing and the pump running, so the symptom is a cold radiator on a warm boiler. The $150-250 covers the visit, the bleed at each radiator and bringing the system back to pressure; a pressure reducing valve that will not hold pressure is a separate part and a separate line on the invoice.
the source prices a service rather than a part - $150-250 to bleed the system and bring it back to pressure - and publishes no part-only figure for it, so the installed band is what stands here
failed circulator pump [S1]
high likelihood advanced $350–$600 installed about 150 min
the radiators never get hot the boiler runs but the house stays cold
The circulator is the part that moves hot water out of the boiler and around the loop, and it is the classic shape of this fault: a boiler that fires, reaches its limit and shuts down while every radiator stays cold. S1 prices the replacement at $350-600 as a minor repair, parts and labour together. S2's Glenside table prices the same job at $375-650, and the two figures are the same company's two published pages rather than a range, so neither is averaged into the other here.
the source prices the fitted job at $350-600, parts and labour together, and publishes no part-only figure, so the installed band is what stands here
zone valve failure [S1]
high likelihood moderate $250–$500 installed about 120 min
the radiators never get hot the boiler runs but the house stays cold
A zone valve is what lets one part of the house have heat while another does not, and its failure reads as a room or a floor that never warms rather than as a boiler fault. S1 prices a single valve at $250-500 fitted and puts the multi-valve case at $800-2,000 or more. S2 prices the same job at $300-550 and adds the local reason the part is common here: many systems in this housing stock were converted from steam to hot water, and the valves that split those conversions into zones are the parts that wear.
priced per valve, fitted: the source quotes $250-500 per zone valve with parts and labour together, and $800-2,000 or more once several have failed together, so the single-valve band is what stands here
failed steam trap [S2]
high likelihood advanced $100–$200 installed about 60 min
the pipes bang and hammer when the heat comes on the radiators never get hot
On a steam system the trap is what lets condensate out and keeps steam in, and S2 gives both the interval and the symptoms: traps fail every 10 to 15 years and the failure arrives as banging pipes, uneven heat and efficiency losses rather than as a boiler that will not run. A single trap is $100-200; a full building survey and replacement is $600-2,000 depending on the count. S2's own warning belongs beside the price - it has seen too many steam systems repaired by technicians who did not understand what they were working on - and S1 says the same thing from the other direction when it tells an owner to make sure the person they call knows steam.
the source prices a single trap at $100-200 and publishes no part-only figure; where a building's traps are surveyed and replaced together it quotes $600-2,000 depending on how many there are
pilot light or ignition failure (thermocouple or ignitor) [S1]
high likelihood advanced $150–$350 installed about 90 min
the boiler will not fire at all the boiler keeps shutting off and restarting
S1 lists this first among its minor repairs: a thermocouple or ignitor replacement at $150-350, fitted. A standing pilot that will not stay lit and an electronic ignition that sparks without lighting look identical at the thermostat, because in both cases the boiler simply never fires and the house goes cold. S2 puts the same item third in its own no-heat sequence, after the thermostat and the breaker, and describes older equipment as having a pilot light and newer equipment as having electronic ignition; the diagnosis is what separates a $150-350 ignition repair from a gas valve at $500-900.
priced as a fitted repair at $150-350 for the thermocouple or ignitor, the source publishing no part-only figure, so the installed band is what stands here
pressure relief valve weeping or stuck open [S1]
medium likelihood moderate $200–$400 installed about 90 min
the pressure gauge has dropped to zero the boiler keeps shutting off and restarting
This is the one number on the page that the same publisher's two separate pages agree on exactly: S1 quotes $200-400 for a pressure relief valve replacement and S2's Glenside repair table quotes the same $200-400. The valve is doing one of two jobs when it drips - holding against pressure that has risen, or leaking because its seat has gone - and either way the boiler loses water and pressure until the low-water cutoff stops the burner. The part is not the diagnosis: the pressure that opened it is what S2 calls a boiler pressure problem, usually a failed pressure reducing valve or air binding.
both cited pages price the fitted replacement at $200-400 and neither publishes a part-only figure, so the installed band is what stands here
waterlogged expansion tank [S1]
medium likelihood moderate $200–$400 installed about 90 min
the boiler keeps shutting off and restarting the pressure gauge has dropped to zero
On a closed hot-water system the expansion tank is what absorbs the water's expansion as it heats; when the bladder inside it fails, the tank fills with water, the system pressure swings with every firing cycle, and the relief valve becomes the part that takes the movement. S1 prices the replacement at $200-400 fitted, and it sits on this page beside the relief valve because the two are the pressure side of the machine rather than the flame side: one absorbs the expansion, the other releases it, and a fault in either shows up on the same gauge.
the source prices the fitted replacement at $200-400 and publishes no part-only figure, so the installed band is what stands here
scale and sediment on the water side of the boiler [S1]
medium likelihood moderate $300–$600 installed about 180 min
the pipes bang and hammer when the heat comes on the boiler runs but the house stays cold
S1 lists a boiler flush and chemical treatment at $300-600. Mineral scale baked onto the heat-transfer surfaces insulates the water from the flame, so the boiler runs longer and hotter to hold the same temperature, the water side gets noisier, and the machine eventually trips its own limit. The efficiency number on the same page is what makes this worth doing rather than tolerating: cast-iron boilers from the 1970s and 1980s run at 70-75% AFUE against 90-95% for a modern condensing boiler, and scale is part of how that gap looks inside one house.
the source prices a boiler flush and chemical treatment at $300-600 as a mid-range repair rather than a part, and publishes no part-only figure, so the installed band is what stands here
failed gas valve [S1]
medium likelihood pro $500–$900 installed about 150 min
the boiler will not fire at all the boiler keeps shutting off and restarting
A mid-range repair in S1's own list at $500-900, and the one on this page that is not an owner job at any price: the valve sits downstream of the gas supply and setting it up is a combustion job. The symptom is a boiler that will not fire at all or fires for a moment and drops out, which is also exactly what a failed ignitor looks like, so the diagnosis is what decides between the $150-350 ignition repair and this one. That is the argument for the visit rather than a part bought on the symptom.
the source prices the fitted replacement at $500-900 and publishes no part-only figure, so the installed band is what stands here
heat exchanger scaled, sooted or cracked [S1]
medium likelihood pro $400–$1,200 installed about 240 min
the boiler runs but the house stays cold the pipes bang and hammer when the heat comes on
S1's own row is heat exchanger cleaning or repair at $400-1,200, and it is the top of the repair column before the machine itself becomes the question. Soot and scale on the flue side cost efficiency the same way scale on the water side does, and on a boiler old enough for the casting to be damaged the same row is the last money worth spending, because the part is the boiler. The source's own parts note applies here rather than at the thermostat: some older boilers need a component sourced through a specialty supplier on a three-week lead time, and three weeks without heat in January changes what the repair is worth.
the source prices heat exchanger cleaning or repair at $400-1,200 and publishes no part-only figure; where the casting itself is gone the part is the boiler, which is the replacement band in the decision block
the boiler is at the end of its life [S1]
medium likelihood pro not priced about 480 min
the boiler keeps shutting off and restarting the boiler runs but the house stays cold
Age plus a quote is the whole test and it is the source's own: S1 says the repair-or-replace question comes up on almost every boiler call with a system over fifteen years old, sets a 50% rule - replacement usually makes more financial sense when the repair costs more than half of what a replacement would - and names the age at which it stops arguing the other way, with a boiler at 25 years and a $1,500 repair. Its efficiency argument points the same way, from the 70-75% AFUE cast iron of the 1970s and 1980s to the 90-95% of a modern condensing boiler, and it prices the answer from $6,000 for a straight residential gas hot-water swap upward. Time basis: no source publishes a duration for a boiler replacement, so the figure here is a book estimate for the swap and not a measured one.
not a repair in either source. S1 publishes the replacement bands instead - $6,000-12,000 for a residential gas hot-water boiler, $8,000-15,000 or more for steam, $10,000-18,000 for a high-efficiency condensing boiler with new controls and $15,000-25,000 for a full system with distribution upgrades - so the replacement figure in the decision block is the price of this cause.
Repair or replace?
The shape of this fault is the source's own sentence: most boiler calls are repairs, not replacements, the repairs are cheap and the replacements are expensive. Six of the twelve causes here are under $600 fitted - a low-water cutoff reset that costs nothing, a bleed and repressurize at $150-250, a thermocouple or ignitor at $150-350, a pressure relief valve or an expansion tank at $200-400 each, a zone valve at $250-500 and a circulator at $350-600 - and those are the ones worth doing at any age. Above them the arithmetic turns, because the same page prices a replacement from $6,000 and sets its own 50% line: when the repair passes half of what a new boiler costs, and the boiler is past fifteen years, replacement is the cheaper answer rather than the more expensive one. The two numbers that decide it are the quote in front of you and the age of the machine, and the source names the age at which it stops arguing: a 25-year-old boiler with a $1,500 repair is money toward a replacement that will be more reliable and cheaper to run, because cast iron from the 1970s and 1980s runs at 70-75% AFUE against 90-95% for a condensing boiler. One thing on this page is not about money at all: a steam system's pressure settings, its water level and its traps are the parts that need somebody who understands steam, and both cited pages say so in their own words. [S1]
- Typical completed repair: $190–$2,375 [S1] — n=29 completed jobs [S1]
- Comparable new unit: $6,000–$12,000 [S1]
- Planning life used for the decision: 25 years
The band above is one published row and it is a mixed one, which S1 says itself: 29 boiler jobs completed between January 2024 and February 2026, a $380 median, middle half $190-2,375, an average of $3,003 and a single most expensive job of $19,726. The source's own reading of the gap is the sentence to keep - most boiler calls are repairs, not replacements, the repairs are cheap, the replacements are expensive, and the average is pulled up by the expensive jobs - and its own table agrees: the three highest single jobs in its location breakdown (Rockledge $15,932, Huntingdon Valley $13,300, Fort Washington $8,810) were full system replacements, one of them including distribution and controls. So the row contains both a $150 thermocouple and a $19,726 new system, and the per-cause prices on this page come from the same page's own repair lists rather than from a cut of that row. The diagnostic fee beside it is the same publisher's Glenside heating table, a different page and a different dataset, and is labelled as such. Two further limits belong in the same sentence, because they are the reason no per-cause count stands on this page: S1 publishes no count and no median for an individual cause on its boiler row - what it prints beside the row is a repair list with price bands rather than a count per repair - and S2's Glenside heating table publishes no count at all, only the band. The per-cause figures here are the two sources' own published repair rows, each named, and no count is claimed for any of them.
The half-of-new-price line falls near $3,000-6,000 against the $6,000-12,000 band S1 publishes for a straight residential gas hot-water replacement, and nothing in the repair column reaches it: the dearest repair row on the page is a heat exchanger at $400-1,200. That is why the decision on this machine is not made by the repair column at all. It is made by the shape of the published row - a $380 median against a $19,726 maximum - because at the top of that row you are not repairing a boiler any more, you are buying one, and the source's own location table shows the three jobs that pulled its average over $3,000 were exactly that. The line to hold against a quote is therefore the 50% rule and the age of the machine, not the median: on a fifteen-year-old boiler with a $2,500 heat exchanger quote, the arithmetic already points at the replacement band.
S1 is the only cited source that puts an age on the decision, and it does it twice: the repair-or-replace question comes up on almost every boiler call with a system over fifteen years old, and the example it uses for when the money is better spent on a new boiler is a 25-year-old machine with a $1,500 repair in front of it. Those are the publisher's own two thresholds, not a measured service life, and no source cited here publishes a measured, sample-based lifetime for a boiler - cast iron from the 1970s and 1980s is still in service in this housing stock, which is the opposite of a life figure. The decision below uses the 25 years the source works to and says that is what it is.
Run your own quote through the calculator — the same half-of-new-price rule with your numbers.
Quick answers
How much does it cost to fix a boiler with this problem?
Completed repairs run $190–$2,375 according to the sources cited on this page, after a diagnostic fee of $150–$180.
How long does a boiler last?
The decision rule used on this page works from a planning life of 25 years.
Repair or replace?
The shape of this fault is the source's own sentence: most boiler calls are repairs, not replacements, the repairs are cheap and the replacements are expensive. Six of the twelve causes here are under $600 fitted - a low-water cutoff reset that costs nothing, a bleed and repressurize at $150-250, a thermocouple or ignitor at $150-350, a pressure relief valve or an expansion tank at $200-400 each, a zone valve at $250-500 and a circulator at $350-600 - and those are the ones worth doing at any age. Above them the arithmetic turns, because the same page prices a replacement from $6,000 and sets its own 50% line: when the repair passes half of what a new boiler costs, and the boiler is past fifteen years, replacement is the cheaper answer rather than the more expensive one. The two numbers that decide it are the quote in front of you and the age of the machine, and the source names the age at which it stops arguing: a 25-year-old boiler with a $1,500 repair is money toward a replacement that will be more reliable and cheaper to run, because cast iron from the 1970s and 1980s runs at 70-75% AFUE against 90-95% for a condensing boiler. One thing on this page is not about money at all: a steam system's pressure settings, its water level and its traps are the parts that need somebody who understands steam, and both cited pages say so in their own words.