How to Replace a Blower on an Outdoor Wood Boiler

The blower fan on an outdoor wood boiler pushes air into the firebox whenever the boiler calls for heat, which lets the fire burn hot enough to bring the water back up to temperature. When the blower motor starts to fail, the boiler keeps running on natural draft but burns cooler and recovers more slowly.

In the video below, Jeff Luff replaces the front blower fan on his own WoodMaster 5500 in the middle of January. With the right tools, the whole boiler fan replacement takes 20 to 30 minutes. This guide walks through the same job in writing, from the first signs of a bad blower motor through rewiring and testing the new fan.

Signs of a Bad Blower Motor on an Outdoor Wood Boiler

A failing blower often gives warning before it quits, either in how the fan starts or in how hot the boiler runs. These are the signs to watch for.

1. The Fan Is Slow to Start

On Jeff's 5500, the first sign was a delay. When the boiler called for heat, the front fan took about 10 seconds to start spinning. Over the next couple of days, that delay stretched to 2 or 3 minutes. A delay that gets longer each day usually means the motor is close to failing, and that was the point where Jeff decided to replace it.

2. The Fan Doesn't Spin at All

If the boiler calls for heat and the fan never turns, the motor may be finished. Before you order a new blower, check the control panel and the snap disc, since a tripped limit control can also keep the fan from running. Our WoodMaster fan troubleshooting guide covers that process. If the motor hums but the wheel won't spin, or makes no sound at all with power reaching it, the blower motor needs replacing.

3. The Boiler Burns Cooler Than Usual

An outdoor wood boiler will still run with a dead blower, because air can flow into the firebox on its own. The fire just burns a lot colder, so the boiler takes longer to reach temperature and may struggle to keep up on cold days. If the fan is running normally and the boiler still burns cool, the firewood is the next thing to check. Our guide on seasoning firewood explains how wet wood affects burn temperature.

How the Blower, Fan Cover, and Laminated Solenoid Work Together

The blower is one of three parts that control airflow into the firebox, and the other two often get replaced during the same job. Knowing what each part does makes the outdoor wood furnace troubleshooting process faster.

• The Blower Fan - The boiler blower fan forces air into the firebox when the aquastat calls for heat. More air means a hotter fire and faster heat recovery.
• The Fan Cover - The fan cover is a rubber flapper that sits over the fan's air opening. When the fan shuts off, the cover drops and seals the opening so air stays out of the firebox between burn cycles. According to the product listing, a good seal saves wood and reduces smoke. The rubber loses its elasticity over time and stops sealing, even when it still looks fine.
  The Laminated Solenoid - The laminated solenoid lifts the fan cover. It mounts on the top of the fan housing and connects to the flapper with a small spring. When the boiler calls for heat, the solenoid pulls the cover open so the fan can push air through. When the call ends, the cover drops back down and seals. The solenoid connects with simple spade connectors, so it is easy to replace during a blower swap if it is worn.

Tools and Parts You'll Need

Having every tool on hand before you start is what keeps this job to 20 to 30 minutes. The hardest part of the job is reaching two of the four mounting bolts, so the open-end wrench matters most.

Tools for Replacing a Blower

• Drill with a 1/4 in driver: for the front cover screws and the fan cover's self-tapping screws
• 7/16 in socket on a 3/8 in drive ratchet: for the two easy-to-reach mounting bolts
• 7/16 in open-end wrench: for the two mounting bolts that are hard to reach
• Needle-nose pliers: for unhooking and rehooking the solenoid spring
• Small flathead screwdriver: for the electrical box cover on the fan
• Small Phillips screwdriver: for removing the beauty ring from the new fan
• Wire cutters: for trimming the new fan's leads
• Gloves

Parts for Replacing a Blower

• Replacement blower: match the model number on the old fan's label. Our wood stove blower fans collection lists each blower by the Dayton or Fasco model it replaces.
• Fan cover: Jeff replaces the cover every time he replaces a fan. The fan cover 2-pack fits the WoodMaster 3300, 4400, 5500, and 6500 and most Dayton fans. It does not fit the FN1TDR3, FN700787, FN800789, or FN900789. The fan cover kits ALT Heat sells include an aluminum strip that holds the rubber flat against the fan and two new self-tapping screws.
• New wire nuts
• Laminated solenoid (if worn): see our laminated solenoids collection for WoodMaster-compatible models.

How to Replace the Blower Fan, Step by Step

The job splits into three stages. You remove the old blower, prep the new fan with a fresh cover, and then install and rewire it. Jeff preps the new fan first, but the steps below follow the order most people will work in.

1. Remove the Old Blower

1. Turn off power to the fan. Shut the fan off at the boiler so it can't start while you're working on the wiring.
2. Remove the front cover. Take out the cover screws with a drill and a 1/4 in driver, then pull the cover off to expose the fan.
3. Remove the four mounting bolts. Use a 7/16 in socket for the two easy bolts and an open-end wrench for the two that are hard to reach. These bolts hold both the fan and the laminated solenoid, so keep them for reinstalling.
4. Unhook the solenoid spring. A spring connects the laminated solenoid to the fan cover. Pop it off with needle-nose pliers.
5. Disconnect the solenoid. Pull the two spade connectors off the solenoid.
6. Disconnect the fan wiring. Loosen the electrical box cover on the fan with a small flathead and undo the wire nuts. There will be two white wires and two black wires. Save the rubber bushing that protects the cord where it passes through the box, since it can be reused.

2. Prep the New Fan and Fan Cover

• Remove the beauty ring. New fans come with a trim ring held on by two small Phillips screws. Take it off and throw it away, because it keeps the fan cover from sitting flush.
• Center the new fan cover. Lay the rubber flapper over the opening as evenly as you can and set the aluminum strip on top.
• Drive the self-tapping screws. Use a 1/4 in driver and stop when the screws are snug. Overtightening pushes the rubber out of shape and breaks the seal.
• Check the seal. Hold the fan up to the light and look for gaps around the cover. Make sure the flapper still moves freely.

3. Install and Rewire the New Blower

• Reconnect the wiring. Move the bushing to the new fan, feed the wires into the electrical box, and connect white to white and black to black with new wire nuts. There is no ground wire on this fan. Trim the leads so the box closes cleanly, and snug the box cover without cranking it down, since too much pressure can push the wires together and cause a short.
• Hang the fan on one bottom bolt. Start one of the bottom bolts first so the fan holds itself in place.
• Mount the laminated solenoid. The solenoid mounts on the top two holes. Start the two easy bolts first, then finish the two hard-to-reach bolts with the open-end wrench.
• Rehook the solenoid spring. Use needle-nose pliers to connect the spring between the solenoid and the fan cover. The angle is awkward, so expect this step to take a few tries.
• Reconnect the solenoid spade connectors. The blower will not work unless the solenoid is connected.
• Route the wire and close it up. Keep the cord clear of the solenoid so nothing catches, then put the front cover back on.
• Restore power and test. On a call for heat, the solenoid should lift the cover and the fan should start right away. When the fan stops, the cover should drop and seal.

How Often to Replace the Fan Cover

The fan cover wears out much faster than the blower motor. Jeff replaces the cover on his own boiler every year, or every other year at the latest. The rubber can look fine after a couple of years and still have lost the elasticity it needs to seal. Because the cover mounts with two self-tapping screws, you can replace it on the existing fan without changing the blower.

Blower Fan FAQs

How long does it take to replace a boiler blower?

The whole job takes 20 to 30 minutes with the right tools. The two hard-to-reach mounting bolts take the most time, and having a 7/16 in open-end wrench on hand speeds them up.

Will an outdoor wood boiler run without the blower fan?

Yes. Air still flows into the firebox on its own, so the boiler keeps burning. It burns much colder, though, and recovers heat more slowly, so replace the fan as soon as it starts to fail.

How much does a replacement boiler blower cost?

Most Dayton- and Fasco-compatible draft blowers in our fans and blowers collection cost between $69.99 and $199.99, depending on the model. A 2-pack of fan covers is $37.98. If you do the work yourself, the parts are the only cost.

Do I need to replace the laminated solenoid with the blower?

Not always. The solenoid comes off with the fan and reconnects with two spade connectors, so you can check it during the swap and replace it then if it is worn.

Shop Replacement Blowers and Fan Covers

A slow-starting fan is the earliest warning that the blower motor is failing, and catching it early keeps the boiler burning hot through the coldest part of winter. Replacing the fan and the fan cover together takes less than half an hour and restores both airflow and the seal between cycles.

Browse our wood stove blower fans to match your current blower by model number, or shop all wood furnace parts for WoodMaster, Central Boiler, and other major brands. For more WoodMaster parts, visit our WoodMaster parts collection.