Londonderry, NH Heat Pump Not Heating? HVAC Fixes

Estimated Read Time: 8 minutes

A heat pump not blowing hot air is frustrating, especially on a New Hampshire morning. Before you panic, work through this simple, safe checklist. You’ll learn why heat pumps sometimes feel cool, how to fix common issues, and when to call a pro. If you want a hand, Paul The Plumber services heat pumps across Nashua, Manchester, Concord, Portsmouth, Dover, Derry, and nearby.

First, know how heat pumps make heat

Heat pumps move heat rather than create it. In heating mode, the outdoor unit extracts heat from outside air and transfers it indoors. That warm air may feel cooler than furnace air because supply temps are often 90–105°F, not 120–140°F. Constant, gentle heat is normal. What’s not normal is no rise in indoor temperature, lukewarm air with the thermostat set higher, or a system that runs nonstop.

Key signals of a real problem:

1. Thermostat shows HEAT but rooms never reach setpoint.
2. Supply vents feel room-temperature after 10–15 minutes of runtime.
3. Outdoor unit is silent while indoor fan runs.
4. Auxiliary or emergency heat runs constantly.

Quick safety and thermostat checks

Start simple and safe:

1. Mode and setpoint: Confirm HEAT mode and raise the setpoint 3–5 degrees.
2. Fan setting: Use AUTO, not ON, so the blower doesn’t push unheated air between cycles.
3. Battery or power: Replace thermostat batteries if present. Check the indoor air handler door switch is closed.
4. Breakers: Inspect the air handler and outdoor unit breakers. Reset once if tripped. If they trip again, stop and call a pro.
5. Emergency heat: If air is cold and you need temporary heat, switch to EM HEAT to run electric or gas backup while you schedule service.

Airflow problems: filters, vents, and ducts

Restricted airflow makes supply temps feel cool and can force long runtimes.

1. Filter: Replace a dirty filter. Many homes need a change every 1–3 months.
2. Vents: Open at least 80 percent of supply and return registers. Don’t block returns with furniture.
3. Duct leaks: Warm air lost in attics or basements will starve rooms. Look for disconnected or crushed flex ducts and whistling joints.
4. Indoor coil: A dust-caked coil reduces heat transfer. If you see ice on the indoor coil, turn the system OFF, set fan to ON for 30 minutes to thaw, then resume AUTO and HEAT. Schedule cleaning if buildup returns.

Signs you fixed it:

• Stronger airflow at vents.
• Supply air feels noticeably warmer after 10 minutes.

Outdoor unit and defrost behavior

In New Hampshire winters, outdoor coils frost up. Your system will run a defrost cycle that briefly pushes cool air indoors. That is normal and should last only a few minutes.

What to check:

1. Snow and ice: Clear 18–24 inches around the outdoor unit. Remove snow drifts, leaves, and pine needles. A buried unit cannot absorb heat.
2. Fan and coil: If the outdoor fan never spins or the unit hums then stops, cut power and call a pro.
3. Long defrost: If you feel cool air for more than 10 minutes or defrost repeats often, a sensor or board may be failing.
4. Heats a bit, then quits: A severely iced coil or stuck defrost can cause short cycles.

What you can do:

• Gently clear loose frost with water from a spray bottle. Do not chip ice with tools.
• Ensure the unit is level and clear of gutter drip lines that re-freeze.

Low refrigerant or a refrigerant control problem

Heat pumps rely on precise refrigerant charge. Low charge reduces heat output and can freeze coils.

Typical symptoms:

1. Longer and longer cycles with poor warmth.
2. Frost or ice on the outdoor unit outside of normal defrost timing.
3. Hissing at lines or oily residue at connections, indicating a leak.

Do not attempt to add refrigerant yourself. A licensed technician should pressure-test, locate leaks, repair, and weigh in the correct charge using manufacturer specs. Using the latest tools and high-quality parts helps ensure lasting repairs.

Reversing valve or control board issues

If air feels cool in both heating and cooling modes, the reversing valve may be stuck. Control board faults or bad defrost sensors can also confuse the system.

What to look for:

1. Thermostat calls for heat, but outdoor unit runs like it is cooling.
2. System toggles in and out of heat randomly.
3. Frequent need to reset power to get heat back.

These faults require proper diagnostics. A pro will verify 24V signals, sensor resistance, and valve operation before recommending repair or replacement.

Auxiliary heat and balance point basics

Most New Hampshire homes have auxiliary heat: electric heat strips or a furnace providing backup when it is very cold outside. When outdoor temps drop, the system may rely on aux heat to maintain comfort.

If your heat pump never feels warm and your bills spike, aux heat may be running constantly due to:

1. Undersized heat pump.
2. Thermostat lockout settings that bring on aux too quickly.
3. Failed outdoor sensor misreporting temperature.

Checks you can make:

• Thermostat settings: Look for heat pump-specific menus. Disable unnecessary aux lockout or widen staging differentials so the heat pump does more work before aux engages.
• Airflow: Poor airflow forces aux heat to carry the load.

Smart thermostat and schedule pitfalls

Smart thermostats are great, but default settings can hurt performance.

1. Recovery time: Aggressive setbacks trigger long recovery using aux heat. Try smaller setbacks, like 2–3 degrees.
2. Equipment type: Confirm thermostat is configured for heat pump with aux heat.
3. Balance and staging: Ensure outdoor sensor is enabled if installed. Update firmware and reconnect any lost Wi-Fi sensors.

Electrical and sensor checks you can safely do

1. Float switch: Many air handlers have a condensate safety switch. A full drain pan cuts heat. Check for standing water and call for service if present.
2. Outdoor disconnect: Verify the pull-out or breaker at the outdoor unit is fully seated and on.
3. Indoor blower: If the blower never starts, listen for a relay click. A failed capacitor or motor needs a technician.
4. Odors or burning smell: Turn off power and call immediately.

When to DIY and when to call a pro

DIY you can do:

1. Replace filters and open vents.
2. Clear snow, ice, and debris from the outdoor unit.
3. Verify thermostat mode, schedule, and equipment settings.
4. Soft reset: Power off both indoor and outdoor units for 5 minutes, then restore.

Call a professional when:

1. Breakers trip again after one reset.
2. You suspect low refrigerant, a leak, or iced coils that return quickly.
3. Outdoor fan never runs or the system frequently enters defrost.
4. You hear grinding, screeching, or smell electrical.

At Paul The Plumber, our licensed, background-checked technicians use modern diagnostic tools to pinpoint the issue, and we use quality replacement parts for lasting repairs.

Preventive maintenance to keep heat strong

A twice-yearly tune-up is the best defense against lukewarm air. Our maintenance visit includes:

1. Thorough inspection for potential issues.
2. Cleaning and lubricating moving parts.
3. Testing electrical connections and refrigerant levels.
4. Replacing air filters to improve indoor air quality and efficiency.
5. Personalized recommendations for optimal performance.

Program perks: Members of Paul’s Promise Plan get priority scheduling, discounted repairs, and consistent service reminders so you never miss a checkup.

Local insights for southern NH homes

Our winters bring freeze-thaw cycles and coastal moisture that challenge heat pumps.

1. Seacoast salt: In Portsmouth and Dover, salt spray accelerates corrosion. Rinse the outdoor coil casing gently each season and schedule coil cleaning.
2. Wind and drifts: In Concord and Derry, drifting snow can bury outdoor units. Install a simple wind baffle or snow stand and keep 18–24 inches clear.
3. Pines and maples: In Londonderry, Salem, and Merrimack, needles and seeds clog coils. Trim vegetation 2–3 feet back for airflow.

Replacement or repair: making the call

Consider replacement if your system is older, uses obsolete refrigerant, or needs frequent repairs. Newer heat pumps deliver better cold-climate performance and may reduce reliance on aux heat.

What we provide with installation:

1. Upfront pricing with options across trusted brands.
2. Expert installation that matches the system to your home’s load.
3. Warranty protection: 2-year parts and labor on heat pump installs, extended to 3 years for club members.

How our techs troubleshoot a no-heat complaint

Our process is methodical so you get answers fast:

1. Interview and thermostat review: We confirm symptoms, recent changes, and thermostat programming.
2. Electrical and airflow: Breakers, disconnects, filter, blower amps, static pressure.
3. Outdoor unit: Fan operation, coil condition, defrost board and sensors.
4. Refrigerant circuit: Superheat, subcooling, and leak checks if readings are off.
5. System controls: Reversing valve actuation and safeties.
6. Final test: Verify steady supply temperatures and correct defrost timing.

We document findings, share photos, and present clear options with no hidden fees. Our team shows up with boot covers and protects your home while we work.

Quick troubleshooting checklist you can save

1. Thermostat on HEAT, set 3–5 degrees higher; fan on AUTO.
2. Replace filter; open supply and return vents.
3. Clear 18–24 inches around outdoor unit; remove snow and ice.
4. Verify both breakers are on; check outdoor disconnect.
5. If coils are iced, turn system off, run fan ON for 30 minutes to thaw, then resume.
6. If no improvement, switch to EM HEAT for comfort and call for service.

Where we serve

We help homeowners across Nashua, Manchester, Portsmouth, Dover, Concord, Derry, Salem, Merrimack, Londonderry, and Hudson. Same trusted support whether you have a ductless mini-split or a central heat pump.

Frequently Asked Questions

Why does my heat pump blow cool air even in heat mode?

Heat pumps deliver air around 90–105°F, which can feel cool compared to a furnace. If rooms never warm, check filters, mode, setpoint, and outdoor frost. Persistent cool air needs a pro.

How long should defrost last on a cold day?

A normal defrost cycle lasts only a few minutes. If you feel cool air for more than 10 minutes or it repeats often, a sensor or control problem may be present.

Should I use emergency heat if my pump is not heating?

Yes, if you need temporary heat. Switch to EM HEAT to run backup heat, then schedule service. Do not rely on EM HEAT long term because it costs more to run.

Can low refrigerant cause no heat?

Yes. Undercharge reduces heat output and can ice coils. Only a licensed technician should test for leaks and set charge to manufacturer specs.

How often should I service my heat pump in NH?

Twice per year is ideal. Seasonal tune-ups catch airflow, electrical, and refrigerant issues early and keep performance strong through winter.

Conclusion

A heat pump not blowing hot air usually comes down to airflow, defrost, controls, or refrigerant. Use the checklist above, then call if comfort does not return. For fast, transparent service across Greater Manchester and the Seacoast, Paul The Plumber can help with diagnostics, repair, or replacement backed by solid warranties.

Call to Schedule

Call (603) 541-7986 or visit https://www.paultheplumbernh.com/ to schedule service today. Ask about Paul’s Promise Plan for priority scheduling, discounted repairs, and extended warranties.

Ready for reliable heat? Call (603) 541-7986 or book at https://www.paultheplumbernh.com/. Get pro diagnostics today and keep your home comfortable all winter.

About Paul The Plumber

For 22+ years, our family-owned team has kept southern NH, the Seacoast, and Greater Concord comfortable with licensed, background-checked HVAC pros. We offer upfront pricing, a 2-year parts and labor warranty on heat pump installs, and a 3-year warranty for club members. We’re BBB A+ rated and known for shoe covers, tidy work, and clear communication. From ductless to whole-home heat pumps, we repair, replace, and maintain systems with quality parts and modern tools.