Boiler Repair in Unionville, PA
Radiators that worked for a century usually need a part, not a new system.
Many of Unionville's village homes and farmhouses still heat with a boiler feeding radiators, baseboard or radiant floors. This page explains how hot water and steam systems work, what cold radiators, banging pipes and odd pressure readings usually mean, and what boiler repairs typically cost.
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Why so many Unionville homes heat with boilers
Unionville's oldest houses were built long before forced air existed. When central heat arrived, many got a boiler and radiators because pipes fit through thick stone and plaster walls far more easily than ducts. A lot of those systems are still running, many now fired by oil.
The Unionville Village Historic District, listed on the National Register in 1979, counts 69 contributing buildings. Its dated landmarks run from the Cross Keys in 1751 to the saddle shop in 1887. Homes from that span were heated by fireplaces and stoves at first, then fitted with boilers later.
The pattern continues past the village. A recent listing on West Doe Run Road, a house built in 1900 on a stone foundation in the Unionville-Chadds Ford School District, was described with oil-fired hot water heat and no central air. That combination is common in local farmhouses.
How a hot water (hydronic) heating system works
A hot water boiler heats water, often to somewhere between about 120°F and 180°F, and a pump pushes it through pipes to radiators, baseboard or floor tubing. The cooled water returns to the boiler to be heated again. The system is sealed and stays full of water under modest pressure.
| Part | What it does | How it usually fails |
|---|---|---|
| Boiler and burner | Heats the water using oil, gas, propane or electricity | Burner lockout, dirty heat exchanger, leaking sections on old cast iron |
| Circulator pump | Pushes water through the loop | Motor hums but won't spin, seized impeller, bearing noise, leaks at the flange |
| Expansion tank | Gives heated water room to expand so pressure stays steady | Loses its air charge and fills with water, so pressure spikes when the boiler heats |
| Pressure relief valve | Opens to dump water if pressure gets too high, often at 30 psi | Drips from high system pressure or a worn seat |
| Fill or pressure-reducing valve | Adds water automatically to keep the system full | Sticks open and overfills, or clogs and lets pressure drop |
| Air separator and vents | Pulls dissolved air out of the water | Clogged vent lets air collect, causing gurgling and cold radiators |
| Zone valves or zone pumps | Send hot water only to the zone that's calling | Motor head fails, valve stuck open or shut, one zone too hot or cold |
| Aquastat or boiler control | Sets water temperature and fires the burner | Wrong settings, failed sensor, no call for heat |
The combination temperature and pressure gauge on the front of the boiler is the most useful thing in the room. Read it cold and read it hot, and write both numbers down before you call.
What should my boiler pressure gauge read?
InspectAPedia lists 12 psi as the typical cold pressure for a residential hot water boiler, rising when the water heats. Its example shows about 17 psi at 185°F as normal. Heating Help notes most relief valves are rated 30 or 50 psi, with the rating stamped on the boiler tag.
Taller houses need a little more pressure, because the water has to reach the highest radiator. Contributors on Heating Help suggest about 12 psi can serve a one-story ranch with a basement, and about 15 psi a two-story Cape. Three-story houses run higher. Your technician sets the right fill pressure for your house.
| What the gauge shows | What it often means | What to do |
|---|---|---|
| Around 12 to 15 psi cold, a few psi higher hot | Normal for most one- and two-story homes | Nothing |
| Near zero or well below 12 psi | A leak, or the fill valve isn't adding water | Look for wet spots and drips. Call for service. |
| Climbs fast toward 30 psi when the burner runs | Waterlogged expansion tank, or the fill valve overfilling | Call soon. The relief valve may start to open. |
| Relief valve dripping or spraying | Pressure too high, or a worn valve | Never cap or plug it. Call for service. |
| Temperature over about 200°F | Control or aquastat problem | Turn the boiler off and call. InspectAPedia flags this as too hot. |
Never plug, cap or tie off a relief valve. It's the last line of defense against a boiler building dangerous pressure. A dripping relief valve is a symptom that something else is wrong.
Steam heat basics: water level, vents and pitch
A steam boiler boils water, and the steam rises on its own through the pipes to the radiators. There it condenses back to water and drains back down to the boiler. That only works if the water level is right, air can escape through the vents, and every pipe slopes back toward the boiler.
Residential steam runs at very low pressure. Heating Help suggests settings that keep a typical system between about one-half and two psi. Higher pressure doesn't heat better. It wastes fuel and makes noise.
Steam still turns up in older village homes and West Chester's older neighborhoods. Fewer technicians specialize in it, so ask when you call.
Steam parts owners should know
- Sight glass. Shows the boiler's water level. It should be partly full, never empty.
- Low-water cutoff. Shuts the burner off if water runs low, so the boiler can't dry-fire.
- Pressuretrol. Stops the burner when steam pressure reaches its setting.
- Radiator vents. Let air out so steam can get in. A stuck vent means a cold radiator.
- Pipe pitch. Pipes slope back to the boiler so condensate drains. A sag traps water and causes banging.
Heating Help advises owners with float-type cutoffs to flush about a quart weekly in heating season if the manufacturer calls for it. The water that comes out is scalding, so use a bucket and gloves, and ask your technician to show you once. Don't move, re-pitch or resize steam pipes yourself.
Boiler and radiator symptoms and what they usually mean
First figure out whether the system is hot water or steam. Most steam radiators have one pipe, one valve and a small vent on the side. Hot water radiators usually have two pipe connections and a small bleed valve near the top.
| What you notice | Hot water system: likely causes | Steam system: likely causes | How urgent |
|---|---|---|---|
| One radiator cold, others fine | Air trapped at the top; closed or stuck radiator valve; zone valve | Stuck or painted-over vent; valve partly closed | Soon |
| Whole house or a whole floor cold | Circulator failed; zone valve stuck; boiler locked out | Low water tripped the cutoff; burner lockout | Same day in cold weather |
| Top-floor radiators cold first | Pressure too low to reach the top; air in high spots | Main vents failed; pressure set too high | Soon |
| Banging, knocking or hammering | Air or a failing pump; kettling from scale inside the boiler | Water trapped in sagging pipes; radiator tilted the wrong way; water level too high | Soon. Repeated hammer stresses fittings. |
| Gurgling or rushing water sound | Air in the lines; clogged air vent | Normal briefly; constant gurgling suggests water level or pitch | Within days |
| Relief valve dripping | Expansion tank waterlogged; fill valve overfilling; worn valve | Rare on steam. Have it checked. | Soon |
| Water on the floor or a damp ceiling | Leak at a fitting, radiator valve, pump flange or boiler section | Leaking return line, radiator valve packing or boiler | Soon. A cracked section can mean replacement. |
| Sight glass empty or murky | Not applicable | Low water, dirty boiler water, clogged glass | Call now. Don't add water to a hot, empty boiler. |
| Soot, oil smell, or a CO alarm | Combustion or venting problem on any boiler | Emergency. Leave and call 911. | |
How to bleed a hot water radiator safely
Bleeding lets trapped air out of a hot water radiator so water can fill it again. It takes a radiator key or a flat screwdriver, a rag and a cup. It only applies to hot water systems, never steam.
- Turn the thermostat down and let the radiators cool for a while. Hot water can scald.
- Start on the lowest floor and work up, farthest from the boiler first on each floor.
- Hold a rag and cup under the bleed valve, then open it a quarter turn.
- Let the air hiss out. Close the valve as soon as a steady stream of water appears.
- Check the boiler gauge when you're done. Bleeding lets out a little water, and pressure should stay in its normal range.
- Turn the heat back up and feel the radiator after the next cycle.
Stop and call instead if
- The gauge drops well below normal after bleeding and doesn't recover.
- You have to bleed the same radiator every week. Air is getting in somewhere.
- The system is steam. Steam radiators don't get bled. Their vents get cleaned or replaced.
- You smell oil, gas or exhaust, or a CO alarm sounds. Leave the house and call 911 from outside.
- An oil burner won't stay lit after you press the reset button once.
Oil, gas and propane boilers, combis and condensing models
The fuel decides most of the burner work, and the boiler design decides venting and efficiency. A condensing boiler only reaches its rated efficiency when return water runs cool, roughly 131°F or below, which some old radiator systems never do.
Oil
The classic farmhouse boiler. Needs a yearly cleaning with a new nozzle and filter, a combustion test and a smoke and draft test. Tanks and lines need watching. Common brands locally include Burnham, Weil-McLain, Buderus and Peerless.
Oil heat repairNatural gas
Where PECO gas lines run, closer to Kennett Square, Longwood and West Chester. Ignition, gas valves and venting cause most repairs. Older gas boilers often vent into a masonry chimney.
Propane
Same burner types as gas but set up for propane. A run-out means a leak check before anyone relights it. Efficiency matters because every gallon arrives by truck.
Propane heatCondensing and combi
Wall-hung condensing boilers from makers like Viessmann and Navien vent through PVC. A combi also makes domestic hot water on demand. They need annual cleaning and their acidic condensate needs a proper drain.
According to Wikipedia's summary, condensing boilers typically reach about 90% efficiency, versus 70% to 80% for conventional designs. Their exhaust is cool enough that they can't use a masonry chimney. Large old radiators can actually help, because big surfaces heat a room with cooler water.
Radiant floors, indirect water heaters, chimneys and CO
Radiant floors
Additions, kitchens and renovated barns often have tubing in the floor fed by the boiler. Radiant loops need much cooler water than radiators, so a mixing valve blends it down. When a radiant zone runs cold or scalding, the mixing valve or its zone pump is the first suspect.
Indirect water heaters
An indirect tank heats your domestic hot water with boiler water through a coil. It's treated as one more zone. If the house has heat but no hot water, look at that zone's pump or valve before blaming the boiler. In summer the boiler fires just for the tank.
Chimney liners
Many village and farmhouse chimneys were built for wood or coal. Oil and gas exhaust is wetter and more acidic, and it can eat old mortar from the inside. A new boiler that vents into masonry often needs a stainless liner sized for it. That belongs in the written estimate.
Carbon monoxide
A cracked boiler section, a blocked chimney or a loose flue pipe can put CO in the house. Pennsylvania's Act 121 of 2013 sets CO alarm rules for home sales and certain rentals. Put alarms on every level and near bedrooms. More in carbon monoxide safety.
Repair or replace a boiler?
A boiler with a sound heat exchanger is usually worth repairing, even when it's old, because pumps, valves and controls are replaceable. Replacement makes sense when a section or heat exchanger leaks, the boiler fails a combustion or CO test, or fuel use keeps climbing.
Replacing a boiler is a chance to rethink the system. Options include a new oil or gas boiler, a condensing model, or adding a heat pump or mini splits to carry the mild months. There's no federal 25C credit for equipment placed in service after December 31, 2025. PECO gas customers can check PECO's gas boiler rebates, which were lowered for applications on or after October 1, 2026. Confirm on peco.com. See replacement options and rebates.
Questions to ask a boiler company
- What's your HICPA registration number, and are you insured?
- Do you work on steam, or only hot water?
- Do you service my brand and fuel?
- Will you check the expansion tank charge and relief valve?
- Will you test combustion and measure CO before you leave?
- If you recommend replacement, will you size it by heat loss, not the old boiler's label?
- Does a new boiler need a chimney liner, and is it in the price?
Look up registrations at hic.attorneygeneral.gov. These apply to any company, including any you're connected with here.
Boiler and radiator questions from Unionville homeowners
Why is one radiator cold when the rest are hot?
On hot water, trapped air at the top of the radiator is the usual cause, and bleeding it often fixes it. On steam, a stuck or painted-over air vent is most likely. If neither helps, the radiator valve or a zone valve may be stuck.
Why do my pipes bang when the heat comes on?
On steam, it's usually water trapped in a pipe that has lost its pitch, or a radiator tilted the wrong way. On hot water, air or scale inside the boiler can cause knocking. Repeated banging stresses fittings, so have it checked.
What pressure should my hot water boiler be at?
Around 12 psi cold is typical for many residential systems, rising a few psi when hot. Taller homes need a bit more. If it climbs toward 30 psi or drops toward zero, call for service.
Why is my boiler relief valve dripping?
Usually the system pressure is too high, often from an expansion tank that has filled with water or a fill valve that's overfilling. Sometimes the valve itself is worn. Never cap it. Call a technician to find the cause.
Can I bleed my own radiators?
On a hot water system, yes. Let the radiators cool, open the bleed valve until water appears, then close it and check the boiler gauge. Steam radiators don't get bled.
How long do boilers last?
Well-kept cast iron boilers often last longer than furnaces. Pumps, valves and controls wear out along the way and get replaced. Damp basements, poor water quality and skipped cleanings shorten their life.
Should I replace my old oil boiler with a condensing boiler?
It depends on your radiators and water temperatures. Condensing boilers reach their best efficiency only when return water runs cool, and they need PVC venting and a condensate drain. A good installer calculates your heat loss and checks whether your radiators can heat the house at lower temperatures.
My house has heat but no hot water. Is the boiler broken?
Not necessarily. If you have an indirect water heater, it runs as its own zone with its own pump or valve. A failed zone valve, pump or tank sensor can stop hot water while the radiators still work.
Does a new boiler need a chimney liner?
Often, if it vents into an old masonry chimney. Oil and gas exhaust can damage unlined chimneys built for wood or coal. Condensing boilers vent through PVC instead, which avoids the chimney but may leave a water heater alone in it.
Is this site a boiler repair company?
No. UnionvillePAFurnaceRepair is a free referral service that connects you with independent local HVAC companies. They set their own prices and terms. This site doesn't perform or guarantee any work and may be paid for referrals.
Sources
- InspectAPedia: Hydronic boiler gauges, pressure and temperature.
- Heating Help: What is the right pressure for a hot water heating system?
- Heating Help: Steam heating dos and don'ts for homeowners.
- Wikipedia: Condensing boiler.
- Listing: 1733 W Doe Run Road (built 1900, oil hot water heat).
- Unionville Village Historic District details, PECO rebate notes and Act 121, as summarized on the Unionville furnace guide.
- Pennsylvania Attorney General: Home Improvement Contractor registration.
Written by Lawrence. Updated October 25, 2026. Facts on this page were checked against the public sources listed above.
This is general information from a free referral service, not a heating contractor. For gas smells or carbon monoxide alarms, leave the house and call 911.
Related furnace help
Radiators cold or pipes banging? Get connected with local boiler help.
Say whether it's steam or hot water, your fuel, and what the pressure gauge reads. Not every heating company works on steam, so it helps to ask up front.
One call to (724) 241-4851 connects you with independent local HVAC companies that serve Unionville and nearby Chester County communities. It's free, with no obligation.
Have this ready when you call
- Your town or road
- Your fuel: oil, propane, gas or electric
- What the system is doing, and any blinking light code
- Whether you smell gas or oil (if so, leave and call 911 first)
Free referral service. Not a heating contractor. Companies are independent and set their own prices.