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Photograph of a modern oil-fired heating boiler Heating System Inspect, Diagnose, Repair

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This page provides our index to building heating system installation, repair, & maintenance.

Here you will find step by step articles describing how to inspect, diagnose & repair residential heating systems: these heating system articles answer questions about all types of building heating systems and describe how to inspect, diagnose, and repair heating system problems, how to cut heating bills, and heating system safety, heating system efficiency and heating trouble-shooting advice.

Our page top photo illustrates a badly rusted gas fired heating boiler.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Heating System Inspection Methods, Diagnosis, Safety, Repairs

Gas furnace schematic (C) Carson Dunlop AssociatesIn these heating system articles we explain how to inspect and detect all defects and hazards on heating systems, boilers, furnaces, and other equipment. Methods for saving on heating cost and on improving heating safety are included.

Heating safety hazards such as carbon monoxide gas leaks, unsafe furnaces, furnace and boiler recalls are addressed.

What kind of heat have I got? 

Start here if you don't know whether your heat is provided by a furnace (hot air) or boiler (hot water), whether your fuel is oil, gas, or electric, and whether your heat is hot water, steam, or warm air:

How do I fix the heating system?

If your heating system is not working properly, choose one of the following diagnostic procedures:

The sketch at above left illustrates basic parts of a conventional gas fired warm air heating furnace; image courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

The heating system inspection, diagnosis and repair articles listed at the MORE READING links at the bottom of this article:

We include product safety recall and other heating system hazards.

Potentially very costly environmental hazards such as leaky oil tanks are explained in depth. Other environmental and indoor air quality topics affected by residential and light commercial heating systems are explored.

To find what you need quickly, if you don't want to scroll through this index, you are welcome to use the page top or bottom SEARCH BOX to search InspectApedia for specific articles and information.

How to Inspect Heating Systems

Oil burner in bath vanity (C) Daniel FriedmanBuilding HVAC (Heating, Ventilating, and Air Conditioning) systems have three tasks: control indoor temperature and humidity at comfortable levels, provide adequate fresh air from outdoors, and the removal of indoor air odors and pollutants by a combination of air pressure control, filtration, and exhaust ventilation systems.

But not all HVAC systems are designed to perform all three of these jobs, and in typical residential buildings, separate and un-coordinated systems may be installed to heat, ventilate, and perhaps cool the building interior.

Start a heating system inspection with basic "distant" visual observations

A proper heating system inspection begins outside with taking notice of the chimneys, flues, and vents, and for the type and location of heating equipment fuel that is used: oil tanks, LP gas, piped in natural gas, solar, etc.

Similarly inside, before attempting a close inspection of the heating equipment itself, take note of and record defects in the heating distribution system (is there even heat present in every room?), and in the location of the heating equipment: is the boiler in a closet where it lacks combustion air, fire clearances etc.

Take a look at the oil burner shown at above left - observed during a mobile home inspection.

From just opening the bathroom sink vanity, we see that an oil burner has been shoe-horned into a space where it does not belong, is unsafe, and is extremely difficult to access and service properly.

See MOBILE HOME HEATING SYSTEMS and

See WALL-MOUNTED FURNACES

Watch out: From the moment of observing work such as the system shown in our photo, the inspector, owner, or heating service technician needs to be on red alert for amateur, unsafe workmanship.

Below and at the links listed at the ARTICLE INDEX the bottom of this article, we provide articles on just about any question you might have about installing, inspecting, troubleshooting, & repairing residential heating systems. Use the Website Search box at page top or the Comments Box at the end of each InspectApedia article to contact us if you cannot find information you need.

For a step by step procedure that can be used to inspect the condition of a heating system, see

HEATING SYSTEM INSPECT DIAGNOSE REPAIR - where we suggest detailed step by step approaches for inspecting complex systems - a free, online, detailed heating system inspection course

Critical Defects in Heating Systems

Sooty gas burner (C) Daniel FriedmanCritical defects which an inspector should not fail to detect when examining any building component or system are defects which form an immediate, significant safety hazard or defects which are quite likely to involve significant repair or replacement cost, and which involve components or systems which are necessary to occupy and use the building.

Methods for detection and diagnosis of these defects are discussed in this document and in its references. Suggestions for inclusion or exclusion of items in this list are invited - see the page top or bottom CONTACT US link.

Because the heating system inspection and related topics discussed here cover a rather broad range, I have not attempted (yet) to list specific critical defects on this summary page.

However any inspection of the condition of heating equipment in buildings must include careful attention to:

Life Safety Hazards:

Watch out: if you see soot on a gas fired heater of any sort - as shown in our gas burner photo above - there is a serious risk of fatal carbon monoxide poisoning in the building. Conditions like this need quick attention and also are a reminder to be sure that both carbon monoxide and smoke detectors are properly installed, located, and tested.

Other examples of what might be serious safety hazards include evidence of unsafe chimneys, missing or damaged safety devices (relief valves, emergency shutoffs), and visual evidence of dangerous overheating of the equipment or leaks of flue gases.

Responsibly conducted, an inspection of a gas-fired furnace, for example, might discover that the furnace has been exposed to severe rust-producing conditions (see our page top photo) which risk an unsafe heat exchanger and a carbon monoxide hazard which could be fatal to building occupants.

Even though the heat exchanger may not be visible, the contextual clues around the furnace, if they are visually obvious, should be translated into a level of concern by the inspector, and where appropriate, translated into a recommendation for action.

This does not mean "failing" every furnace to be on the "safe side", it means responsible inspecting and reporting.

See EXPLODING RADIATOR for a reader's question about a possible example of a dangerous condition that may not have been recognized.

Costly defects:

Such as evidence of a heating system at or near the end of its life of safe, reliable operation, or evidence of a buried oil tank which is likely to be old and for which there is no record of leak testing, should be reported.

Heating System Inspection & Diagnosis Detailed Articles & Education Curriculum Suggestions

See key heating system inspection, troubleshooting, installation or repair articles at the MORE READING article recommendations found at the end of any article at this website.

Defect Lists & Education Curriculum suggestions: for heating system inspection, troubleshooting, repair

How to Reduce Home Heating Costs

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

How do I fix a cold steam radiator?

I have steam heat on two floors. The 2nd floor gets too hot and has 6 one pipe radiators with angled steam valves attached. The first floor has 3 radiators. They are all two pipe radiators and they all have angled steam valves like the ones on the second floor.

The smallest radiator on the first floor gets hot and so does the farthest large radiator. The radiator closest to the boiler on the first floor, which is large, does not get heat. Up to its supply valve i get close to 100 degrees while the rest of the radiator is cold.

Upstairs the one pipe radiators are all too hot and avery about 150 degrees at the same time. In the basement not far from the boiler the main return has a Gorton main steam valve.

Why can't i get heat to the large radiator on the first floor? Can i use TRVs to regulate the heat on the second floor? - On 2022-12-27 by Z11542

Reply by InspectApedia Publisher - Why can't I get heat to the large radiator on the first floor?

@Z11542,

When some steam radiators on a piping loop get hot and others don't, I suspect a closed or jammed radiator valve, a clogged or defective steam vent, or on occasion a problem with blocked condensate return.

The fact that one of your rads gets hot on one end suggests that it's having trouble returning condensate. An experienced plumber or heating service tech may be able to dis-assemble and clean the rad bottom or pipe connections, but that's a bit inconvenient in the middle of cold weather.

And yes, for more-careful control of individual radiator heat output you can certainly install thermostatic radiator valves (TRVs) on any of your radiators. Again, not so convenient to do during the heating season, but if you've got enough work to make the job interesting to a heating service company they might be willing to send enough experienced technicians to first survey for what's needed, then return to do the job quickly enough that you don't freeze.

Start at STEAM HEAT RADIATOR REPAIR - diagnose & repair - for cold steam heat radiators.

Our complete guide to heating radiator troubleshooting and repair starts at

RADIATORS for ROOM HEAT - home

 

Rheem Centurion II AC/Heat split unit Blower Wont Run

I have a Rheem Centurion II AC/Heat split unit and my blower wont run. I replace 24V power supply about 3 months ago because thermostat quit working, fixed that.

Now that blower stopped running, I've replaced blower motor, capacitor, and control board and it still wont run. What else is there to check/replace? - On 2022-12-22 by Jamie

Reply by InspectApedia (Editor) - Rheem Centurion II AC/Heat split unit blower won't run

@Jamie,

First, before doing anything else, check the air handler access cover door interlock switch.

That switch will keep the blower off even if nothing else is wrong.

Then if that doesn't fix the trouble see our diagnostic procedure

at BLOWER FAN WONT START 

Followup by Jamie

@InspectApedia (Editor), As far as I can tell, its working [the blower door switch].

I hold it in when i'm inspecting things and everything appears to work except the blower.

Gas blower and system seems to start but won't continue because blower isn't running. Have 2 green lights on the control board that come on.

Reply by InspectApedia (Editor) - check that voltage is being delivered to the blower

@Jamie,

You checked that voltage is being delivered to the blower, right? With all that new stuff I'd then suspect that either we've missed a control that's keeping the blower off or a wiring error.

The fan limit switch has to be wired right and working

And if the furnace's fuel is gas and there's a spill switch that has to be working and not tripped, etc.

In normal operating sequence, if the burner runs but the blower fan doesn't start check

again the diagnostics at BLOWER FAN WONT START  - look at steps 5 through 12.

You can leave the thermostat out of the equation by removing the tt wires at the air handler and jumpering the 2 T T terminals - that's what the thermostat does on a call for heat.

Then if still needed, step through all of the diagnostic checkpoints at

NO HEAT - FURNACE

 

Where is the furnace on my Keeprite CDGI125AH01 Furnace?

I purchased a home back in early september. November was cooler, december is -26c tonite.

I checked the furnace for a filter, to which I cannot find. I am asking if anyone knows if this furnace has a filter and where it might bt located. It is not near the blower or anywhere.

The make of the furnace is a Keeprite, model cdgi125ah01. Thank you. - On 2022-12-07 by LORI

Reply by InspectApedia (Editor)

@LORI,

If there is no air filter at the furnace air handler return air plenum then it may be located in a ceiling or wall central air return inlet.

See our tips on how to find the furnace filter

at AIR FILTER LOCATION

Or if there really is no air filter on your system, then

see MISSING / LEAKY AIR FILTERS

 

I Need a manual for old Sears Furnace 867.762130

Would anyone out there happen to have access to a manual for an old sears furnace model 867.762130? Any help greatly appreciated. - On 2022-11-30 by Ep

Reply by InspectApedia (Editor) - old sears furnace manuals

@Ep,

Check our SEARS HVAC MANUALS page of PDF downloads

 

On 2022-11-17 by Susana

@InspectApedia (Editor), thank you - service co adjusted the dip switches to lower air flow settings. Dampers are working properly per tech, and they suggested adjusting lower level zone damper's closed position to let some pressure off of system if the adjustment didn't do enough.

Our 23 year old furnace was propabably bogged down, too. Thank you again for the help and web link!

Reply by InspectApedia (Editor) - AIr handler blower speed too high - air flow "too strong" at supply registers?

@Susana,

Thanks back to you for following-up with what worked. That will help other readers:

AIr handler blower speed too high - air flow "too strong" at supply registers?

Check fan speed settings on dip switches or jumpers on the air handler control board

Check/adjust position of duct dampers to be sure you've got the right balance of air flow among different duct zones.

 

 

Is our new furnace blower too powerful for the old dampers in our ductwork?

We had a new 100,000btu furnace installed. Our heating system is controlled by our original Carrier Comfort zone thermostat and control board (5zones) with electric 3 wire dampers.

After installation of new furnace heat is pushing through closed dampers - tabs indicate in closed position but air is being forced through. Some whistle. Basement set at 65, but is 69 degrees.

Can the new furnace be too powerful for the 22 year old dampers?

Does the furnace have settings to adjust?

Never had this issue prior to new furnace install, zone temps always maintained, never more than 1 degree warmer than setting.

Afraid service company will try to tell me i need to spend 1,000s in new equipment when in fact they did not match my existing components with furnace. Thank you for the help! - On 2022-11-13 by Susana

Reply by InspectApedia (Editor) - Carrier Comfort zone thermostat and control board

@Susana,

Heating and air conditioning Air Supply registers are never absolutely airtight. It's normal for there to be some air leakage through them when the fan and the air handler is running.

However if you think that the airflow is stronger than you like and noticeably stronger than it was with the previous air handler there are two explanations that should be understood:

First, it's possible that the squirrel cage fan in the blower of your old air handler was dirty.

Dirt on those fan blades can cut the air flow output by 60 or more percent. So a new blower with a clean fan will definitely move much more air.

Second, many air handlers have a fan speed setting that can be adjusted. It may be on a control board.

Often the air handler uses a different speed when cooling then when heating.

So you want to review those settings with your installer to be sure they are correct.

And yes, on many air handlers there is a control board with jumpers that can change the fan speed if necessary.

Followup by Susana - Is there any reason to believe the damper vane's failing ?

@InspectApedia, Thank you for the suggestions.

Is there any reason to believe the damper vane's failing - can it show closed but be letting a lot of air through?

We could swap the damper inserts to see if the added heat shows up in corresponding zone.

Reply by InspectApedia (Editor) - duct damper failure causes abnormal air flow at some air supply registers?

@Susana,

Thanks that's an interesting question - duct damper failure causes abnormal air flow at some air supply registers?

Duct damper vanes never close off a duct completely since making them that air-tight would either jam the moving baffle in the duct or would make the product more expensive than the manufacturers think they can sell.

Let's try a simple test: for an HVAC system air supply register that is downstream from the duct damper, try the duct damper in it's OPEN position and then in its CLOSED position with, of course, the air handler blower running. You should feel a significant drop in airflow when the damper closes.

See details at ZONE DAMPER CONTROLS
And let us know what you find.

 

How much can I reduce the flue pipe on my wood burning furnace?

For a wood burning furnace, what is the minimum size allowed to reduce a flue pipe from an 8 inch exhaust to an outside chimney? Thanks in advance for any response. - On 2022-10-25 by haley

Reply by InspectApedia (Editor) - minimum size allowed to reduce a flue pipe

@haley,

You would not normally make ANY reduction in the exhaust flue or vent piping lest you create a draft or safety problem for your furnace. So before squeezing down the vent connector between the wood-fueled furnace and the chimney itself, check with the furnace manufacturer.

At the very least I suspect they'll tell you about a requirement to measure/assure adequate draft.

 

Fraser Johnston Furnace 1960, Model 45-CJDS - need information and manual

I have an old Fraser-Johnston furnace with a typewritten tag taped on it that says it was new in 1960, Model 45-CJDS, Serial 295438.

The unit dimensions are Height: 60 inches, Width: 8 inches, and Depth: 27-3/4 inches.

There is no manufacturer’s tag on the unit. I would welcome any comments or information. - On 2022-10-15 by Tom

Reply by InspectApedia (Editor) - old Fraser-Johnston furnace

@Tom,

Please see your question re-posted along with our reply now at

FRASER JOHNSTON HVAC

 

Why is there soot on the heat exchanger if the building air and oil burner exhaust are separate?

If oil furnace combustion chamber gases and the air passing over the heat-exchanger are separate, assuming NO cracks in combustion chamber or exchanger, why should there be any soot on the heat-exchanger?

I'm having trouble visualizing the actual physical relationship between these two oil furnace components.
Thank you. - On 2022-10-12 by Richard Garcia

Reply by InspectApedia-911 (mod) - soot is a natural product of oil burner combustion

@Richard Garcia,

Thank you that's a helpful question.

To be more clear, we should understand that the soot is a natural product of oil burner combustion, and forms or collects inside the heat exchanger and thus in the passages through which combustion gases are passing.

In sum:

You would NOT expect soot formation on the exterior of the heat exchanger over which building air is passing.

But soot formation inside the heat exchanger during oil burner operation is normal - and explains why an annual service and cleaning are very important for oil fired furnaces.

Watch out: if you are seeing oil burner soot forming on the outside of the heat exchanger then there is either a possibly dangerous heat exchanger leak or the oil burner is not working properly and is blowing soot around the utility room and furnace. Service and inspection would be needed promptly.

 

How to wire a Hardy wood boiler to the A/C and furnace

I am needing to wire a hardy wood boiler to the ac and furnace. There are 3 wires on a hardy that need to be connected through relays. Any suggestions? - On 2022-09-04 by aw

Reply by InspectApedia-911 (mod)

@aw,

Let's start with the specific model and it's manual.

Can you tell us or better, post a photo of the heater's data tag.

Just telling me there are three wires without identifying where each is routed (what it does) is not enough information to proceed.

Proper safety control setup is critical, too.

Followup by aw

@InspectApedia-911, I don’t have a model. I am needing the wiring from boiler to ac for the relay.

This is where I’m stumped. Hardy h6. Needing to make sure it is wired from thermostat to relays. I know one goes to 7 and 8 on the relay. I have a 3 wire thermostat.

all hardy wood boilers are the same. They have a 3 wire that needs to be connected to relays.

I have spent hours looking for diagrams on this. Hardy manufacturer diagram does not have what I am needing.

I need to know how the relays need to be wired on a 90340 relay for the ac part without using an aqua stat.

Reply by InspectApedia-911 (mod) - Wiring details for the White Rodgers 90-340 Control Relay: schematic and instruction manual here

@aw,

We've posted a typical wiring diagram for the White Rodgers 90 340 control relay wiring just below,

And here is the White Rodgers 2 POLE SWITCHING RELAY 90-340 INSTRUCTION SHEET [PDF] courtesy of sidharvey.com (we saved a backup copy as White-Rodgers-90-340.pdf) but

90 430 Control Relay typical wiring diagram cited & discussed at InspectApedia.com

Watch out: I think the reason you may be having trouble with this wiring setup, and the reason that the manufacturers may be not providing you the detail that you ask, is that there are some serious safety and control issues in trying to coordinate multiple, different fueled heating systems.

I understand that you want to reduce the question to something very simple such as 'just tell me where to put the wires'.

But the fact is we have no information about the various pieces of equipment, fuels, and venting or even nearby construction materials for your installation.

Some very basic questions such as whether or not a flue is shared involves major safety and fire hazard questions.

So just answering someone's question who, understandably impatient, says "never mind all that, just tell me where to put the wires" leaves people who are sitting far away nervous about the safety of the installation.

So what I would do in this case is to call the manufacturers technical support people directly, they can ask you questions about your installation and then offer a more technically correct and safe answer.

 

Diagnose rattling popping noise at new Lennox furnace

New Lennox furnace installed January 2022 - over the last week I've noticed a rattling or popping sound within the unit when the burners ignite.

We're getting heat in the house, but don't want it to be another heat exchanger issue. - On 2022-02-02 by Dylan

Reply by Inspectapedia Com Moderator - rattling or popping sound in the Lennox furnace

@Dylan,

Some rattles or popping noises could be normal at your furnace, others, signs of trouble.

With just the noise description no one with any field experience would pretend that they knew what was going on, but indeed there are some things you can check.

Take a look at the diagnostics at

GAS BURNER POPPING NOISES

and let me know what you find on your system.

...

Continue reading at BOILER CONTROLS & SWITCHES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HEATING SYSTEM FAQs - questions & answers posted originally in this article

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Suggested citation for this web page

HEATING SYSTEMS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING SYSTEMS

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