Wood Chip Boiler Troubleshooting: Fault Codes & Auger Jams

A wood chip boiler that stops working in the middle of winter is more than an inconvenience — it can halt heating across an entire property in hours. Whether you manage a farmstead, a rural home, or a commercial facility running on biomass heat, this guide is built around one job: finding the fault fast. It covers how the system works, which symptoms point to which cause, how to clear the most common faults step by step, and how to stop them coming back.

Accurate diagnosis starts with a clear picture of what the machine does and how its parts depend on each other. Attempting a repair without that foundation often leads to misdiagnosis — and sometimes makes the fault worse. A few minutes spent understanding the system can cut troubleshooting time from hours to minutes.

A common point of confusion is worth settling first. A "wood chip boiler" in the sense used here is an automated, auger-fed system: chips move from a hopper or silo through a conveying mechanism into the combustion chamber, with feed rate, ignition and airflow controlled by a control panel. This is a different machine from a traditional "outdoor wood boiler" (OWB), which is usually loaded by hand with cordwood or logs and relies on a simple water jacket, circulator pump and aquastat rather than an auger and lambda sensor.

If your symptoms involve water temperature not rising, a circulator pump not running, or a solenoid/damper issue, you probably have a manually-loaded cordwood boiler, and the fault-finding approach differs — those problems sit on the water and electrical side. This guide covers automated wood chip systems, where most faults begin in fuel handling and combustion control rather than in the water circuit.

A woodchips boiler is built from several integrated components, each with a specific role. The fuel store — typically a hopper or silo — holds the chip supply. From there, a conveying system (usually an auger or chain conveyor) moves the chips toward the combustion chamber.

Inside the chamber, a grate or retort burner ignites the fuel and a heat exchanger passes the thermal energy to your heating circuit. A lambda sensor measures oxygen in the flue gas and trims airflow automatically to hold efficiency. An ash removal system, manual or automatic, clears residue from the burn area.

The control panel ties it all together, running the logic for fuel feed, fan speed, ignition cycles and safety shutdowns. Knowing which component owns which function is the first step toward targeted fault-finding.

Fuel flow depends on consistent chip size, moisture content and mechanical clearance. Chips leave the hopper and enter the primary auger, a rotating screw that pushes material along a horizontal or angled channel toward the burner. In larger systems a secondary auger or stoker then feeds the combustion zone at a controlled rate, measured in kilograms per hour against heat demand.

The control unit adjusts this feed rate continuously. If chips are oversized, too wet, or the channel is partly blocked, the flow rate drops and the boiler either underfires — delivering less heat than demanded — or raises a fuel-feed fault and shuts down. Even a 20–30% partial obstruction can be enough to trigger error codes or inefficient combustion.

Most faults are downstream effects of an upstream cause. Poor combustion, for example, is rarely a faulty burner; it is far more often wet fuel entering a burner that works perfectly. Likewise, repeated ignition failures often trace back to auger timing rather than the igniter itself.

Once you can follow the sequence from hopper to heat exchanger, you can trace a fault upstream to its real origin instead of replacing parts that are fine. It also helps you describe the problem clearly to service engineers, which shortens callouts and diagnostic fees. Experienced biomass installers will tell you that most of their callouts involve something preventable that the operator could have spotted earlier.

Wood chip boilers are robust, but they process raw biomass continuously over long heating seasons. Some faults occur far more often than others, and most follow recognisable patterns. Knowing the symptom and the usual cause puts you well ahead of the problem.

Ignition failure is one of the most reported problems in wood chip boiler operation. The boiler tries to start, fuel reaches the burner, but combustion never establishes and the system locks out with an ignition fault. The most common cause is a failed or degraded ignition element, which typically lasts 500 to 2,000 ignition cycles depending on the manufacturer.

Wet fuel is the other usual suspect: chips above 35% moisture are extremely hard to ignite even with a healthy element. Air supply problems — a blocked intake or faulty combustion fan — are also frequent, because the burner needs a precise air-to-fuel ratio of roughly 6:1 by mass for clean ignition. Check the element, fuel moisture and fan operation before assuming the control board is at fault.

When a boiler runs but misses its rated output — say 40 kW from a 60 kW system — the cause is almost always combustion quality. Incomplete combustion shows up as dark, sooty flue gas and a persistent smoke smell. It happens when the air-to-fuel ratio is off, usually from a dirty lambda sensor giving false oxygen readings, a partly blocked heat exchanger reducing flue draft, or fuel with a lower calorific value than the system expects.

Chips at 30% moisture hold roughly 25–30% less usable energy per kilogram than chips at 20%. A dirty heat exchanger compounds the loss: just 3mm of soot on exchanger surfaces can cut thermal transfer efficiency by up to 10%. Regular cleaning and fuel quality control are the main remedies.

Auger jams happen when material physically obstructs the conveyor and fuel cannot reach the burner. Typical causes are oversized chips — ideally within the G30 class, meaning particles no larger than 30mm — or wet, clumped material that bridges across the channel and forms a solid plug. Foreign objects such as stones, wire or bark strips cause sudden jams.

The tell-tale sign is a fuel-feed fault code, often alongside a motor current spike on systems with smart diagnostics. Left unresolved, a jam can overheat the auger motor or damage the screw. Always isolate power before clearing a blockage by hand.

Also check that hopper material is within specification and that no bridging is forming above the auger inlet, which can happen with fine or damp chips even when the auger itself is clear.

Speed matters when the boiler is down, especially in cold weather when a property depends on it for space heating and hot water. Most common faults can be cleared in 30 to 90 minutes by a confident operator without specialist tools. The key is to work through a logical sequence rather than trying several fixes at once.

Isolate the boiler from the mains supply and wait at least five minutes for residual heat in the combustion area to dissipate. Open the auger access panel — usually at the side or base of the unit — and inspect for the blockage. Use a rigid brush handle or wooden dowel to break up clumped material; never use metal tools near the auger flighting, as they can damage it.

Remove the blockage in sections, working from the outlet back toward the inlet. Once the channel is clear, check the chips in the hopper: if they are visibly wet or contain oversized pieces, remove and replace them before restarting. Then re-engage the auger manually (most units have a jog function on the control panel) to confirm it runs freely before a full restart.

Record the time, fault code and chip condition in your maintenance log.

Modern wood chip boilers use fault codes to show which component or process triggered a shutdown. Never reset a code before identifying and fixing the cause — repeated resets can mask a developing problem and cause secondary damage. Once the root cause is dealt with, open the fault log on the control panel, confirm the fault no longer shows as active, and perform a manual reset following your boiler's manual.

Most systems need a 10–15 minute cooldown between ignition attempts. After restart, watch the first burn cycle closely: confirm the auger feeds at the correct rate, the flame establishes within the expected window (usually 3–8 minutes), and flue gas temperature climbs steadily into the operating range of 150–250°C. If the fault code returns in the first cycle, do not reset again — investigate further or contact your service provider.

Some faults are beyond what an operator should tackle alone. Repeated ignition failures across several fuel batches, persistent combustion faults after cleaning and fuel changes, or error codes tied to the lambda sensor, control board or heat exchanger integrity all call for a certified biomass engineer. In the UK, look for engineers registered under the Microgeneration Certification Scheme (MCS) or accredited by the manufacturer.

Elsewhere, check whether your boiler is under a service contract — many manufacturers require annual professional servicing to keep warranty cover. Safety-related faults, including CO alarm activation, flue backdraft or pressure relief valve discharge, should never be self-diagnosed. Shut the system down immediately, ventilate the area, and call a professional before running the boiler again.

One of the most overlooked causes of wood chip boiler problems is a mismatch between fuel and boiler specification. Chips and pellets are not interchangeable, and using the wrong type — or a chip grade outside your boiler's rating — produces predictable, recurring faults. This section shows how to read those faults back to the fuel.

Moisture content is the single most critical fuel variable in a chip boiler. Unlike wood pellets, which are manufactured to a standard 8–10% moisture, chips arrive from forestry and arboricultural work at widely varying levels — often 20% to 55% depending on seasoning and storage. Most chip boilers are designed for 20–35% moisture (M20–M35 under EN ISO 17225-4).

Above 35%, the fuel needs far more energy to dry before it burns, which cuts net output, raises emissions and causes incomplete combustion that deposits tar in the flue. A handheld moisture meter costing £30–£80 lets you check every delivery before it enters the hopper — an investment that pays for itself quickly in avoided faults.

Chip fuel is classified by particle size under EN ISO 17225-4, from G30 (up to 30mm) through G50, G100 and beyond. Your boiler's manual states the maximum chip class; material coarser than rated is a leading cause of auger jams and combustion problems. Ash content matters too: softwood chips typically give 0.5–1.5% ash by dry weight, while contaminated or bark-heavy chips can reach 3–5%, demanding more frequent ash removal and raising the risk of clinker on the grate.

The table below summarises key quality parameters and recommended ranges for standard residential and light commercial wood chip boilers.

Some operators run pellets through a chip system, or the reverse, to save money or because their usual supplier is out of stock. It is a common source of sudden faults. Pellets are denser, smaller and more uniform than chips, so they travel through a chip auger much faster, delivering more fuel per rotation than the control unit expects. The result is overfiring and potential damage to the combustion chamber.

In the opposite direction, a pellet boiler fed coarse chips will jam its finer auger almost immediately. Some modern boilers are marketed as dual-fuel, but that needs specific hardware, including interchangeable feed modules and updated control firmware. Confirm compatibility with the manufacturer before changing fuel type, and never mix chip grades or blend pellets with chips in a non-rated system.

The term woodchip biomassa refers to wood chip used as a biomass energy feedstock, and its quality largely decides whether a boiler runs cleanly or keeps faulting. Poor-quality biomass does not just reduce performance; it causes progressive mechanical and thermal damage that shortens service life and raises maintenance costs year on year.

Several symptoms point squarely at fuel. Dark, sticky tar or resin on the inside of the flue pipe means combustion temperature has been persistently too low, usually from excess moisture. Clinker (fused ash on the grate or in the chamber) suggests high ash content or contamination with soil, stone or mineral material.

Ash removal needed more often than your schedule specifies also signals elevated ash. If seasonal efficiency has slipped from a rated 85–90% toward 70–75% and cleaning and tuning have not recovered it, degraded fuel is the likeliest explanation. Asking your supplier for an EN ISO 17225-4 compliance certificate with each delivery is the most reliable way to verify what you are actually burning.

This section looks only at storage as a boiler-fault issue; general chip storage practice is covered in our separate storage guide. For a boiler, the practical risk is moisture creeping back into chips that passed inspection on delivery. Wood chips absorb atmospheric moisture quickly, especially fine fractions, and chips kept in a poorly ventilated or open store can gain 10–15 percentage points of moisture in a few weeks of wet weather.

Keep the store covered and ventilated with a sealed floor, and cap pile depth at 3–4 metres to avoid self-heating. Use first-in, first-out so older chips are burned first, and re-test moisture at the hopper if material has sat for more than a couple of weeks. Discard visibly mouldy chips: they carry less energy and more fines, both of which show up as feed and combustion faults.

The most effective single measure against recurring faults is a simple acceptance routine at the point of delivery, backed by a supplier who provides traceable, specification-compliant material. Schemes such as Woodsure Ready to Burn (UK) or equivalent national assurance programmes mean batch data on moisture, particle size distribution and ash is available when you need it.

Build a delivery checklist: moisture meter reading on arrival, visual check for oversized pieces or foreign material, and a record of the chip class supplied. Over time this data shows whether quality holds across seasons, and it gives you evidence if a non-compliant batch causes a breakdown and you need to make a claim.

For buyers sourcing internationally, exporters such as PT. Haafa Wirama Lestari supply wood chips processed to defined moisture and particle-size specifications for industrial biomass boiler applications — the same specification discipline applies whether fuel is sourced locally or imported by container.

The best way to handle boiler faults is to prevent them. A structured routine carried out at daily, weekly and annual intervals sharply reduces unplanned downtime, extends component life and keeps the system at rated efficiency all season.

Daily checks take under ten minutes and catch most developing faults before they become shutdowns. During the heating season, confirm the hopper is adequately stocked, check the control panel for active fault codes or warnings, and verify flue gas temperature is in the normal range in your manual (typically 150–220°C at steady state). Weekly, empty the ash drawer or box — even with automatic removal, a manual check prevents overflow — clean the viewing window on the combustion chamber door, and inspect the auger inlet for bridging or damp material.

Run your hand along the accessible flue pipe to feel for unusual hot spots, which can indicate a partial blockage forming inside. Log every check with the date and any observations, even when all looks normal.

An annual service, ideally at the end of the heating season or just before autumn, covers the deeper tasks that protect long-term reliability. Clean the heat exchanger thoroughly with the manufacturer's recommended brushes and, if needed, a chemical flue cleaner to remove carbonised deposits. Inspect the lambda sensor and replace it if degraded — most have a service interval of 4,000–6,000 operating hours.

Test the ignition element under load and replace it if resistance is out of specification. Check the combustion chamber refractory for cracking or erosion, since damaged lining lowers combustion temperature and speeds heat exchanger wear. Service all moving parts in the feed system — auger bearings, gearbox oil level, conveyor chain tension — to manufacturer intervals.

Annual service typically costs £250 to £600 depending on boiler size, a fraction of a single emergency callout for a preventable fault.

A fault log is among the most underused tools in boiler management. Each time a code appears — even if you clear it quickly — record the date, the code, operating conditions, the fuel batch in use and what you did. Over a season, patterns emerge that would otherwise stay hidden: a code that recurs only in cold snaps may point to fuel moisture rising when outdoor storage temperatures drop; a jam every six to eight weeks suggests an auger bearing nearing end of life.

Simple spreadsheets or dedicated biomass management apps make logging easy. Handing the log to a service engineer at annual service gives context that visual inspection alone cannot, and it often cuts diagnostic time from hours to minutes. A well-kept log is also valuable evidence if a component fails under warranty.

Q: Is a wood chip boiler the same as an outdoor wood boiler?

A: No. A wood chip boiler is an automated system that conveys chips from a hopper via an auger into the combustion chamber, controlled by a control panel and lambda sensor. A traditional outdoor wood boiler (OWB) is typically loaded by hand with cordwood and relies on a water jacket, circulator pump and aquastat. If your issue involves water temperature, a circulator pump, or a solenoid/damper, you're likely dealing with the latter, and the troubleshooting steps differ from those in this guide.

Q: What is the most common problem with boilers?

A: For wood chip boilers specifically, the most common problem is a fuel feed fault — either damp or oversized chips jamming the auger, or poor-quality material that prevents clean ignition. In general heating boilers, low pressure and ignition failure are the most frequently reported issues. Both are typically resolved through straightforward maintenance rather than component replacement.

Q: Why is my boiler taking so long to heat up?

A: Slow heat-up in a wood chip boiler is usually caused by wet fuel lowering combustion temperature, or a dirty heat exchanger limiting heat transfer to the heating circuit. Check chip moisture with a handheld meter and clean the heat exchanger surfaces — in most cases one or both actions will restore normal warm-up times.

Q: Why is my boiler losing pressure but no obvious leaks?

A: Pressure loss without a visible external leak often points to a faulty pressure relief valve releasing small amounts of water under load, a micro-leak at a fitting inside the boiler casing, or air entering through a poorly sealed expansion vessel. A heating engineer can pressure-test the system to isolate the cause — do not leave this unresolved, as sustained low pressure causes pump cavitation and heat exchanger damage over time.

Q: How to make a wood boiler more efficient?

A: The most impactful steps are keeping fuel moisture consistently below 30%, cleaning the heat exchanger at least once per season to remove soot build-up, and verifying the lambda sensor is calibrated so the air-to-fuel ratio is optimised. Running the boiler at or near rated output — rather than at low partial loads — also improves seasonal efficiency, as biomass boilers perform best in their designed power band.

This article provides a detailed guide on "Wood Chip Boiler" for everyone, helping to identify and resolve common faults quickly to save time, money, and discomfort. By understanding how the system works and its components, readers can diagnose and fix problems efficiently, keeping their wood chip boiler running reliably long term.

About the author: This guide was written by Gideon "Ibrahim", Director and Founder of PT. Haafa Wirama Lestari, an Indonesian exporter of wood chips, wood pellets, rice husk pellets, and cocopeat to industrial biomass buyers. Because fuel moisture, particle size, and ash content are the root cause of most of the faults covered in this guide, quality-controlled sourcing is one of the most direct ways operators can reduce boiler downtime.