--- title: "Furnace and Hydronic Heat Repair | Rancho Santa Margarita" description: "Suburban NT series furnaces, sail and limit switches, Truma Combi and AquaHot hydronic systems diagnosed and repaired in shop at $260 per hour." focus_keyword: "furnace and hydronic heat repair rancho santa margarita" canonical: https://ocrv.me/services/appliance-repair/furnace-and-heating-system-repair/ kind: subService updated: 2026-07-29 source: OCRV Center --- # Furnace and Hydronic Heating System Repair for Coaches > A furnace where **the blower runs and no flame arrives** is usually a sail switch or a voltage problem. Heating work runs **$350 to $8,500+** at $260 per hour. ## What does RV furnace and heating system repair cover? Heating repair covers forced air furnaces such as the Suburban NT series, combination units like the Truma Combi, and diesel fired hydronic systems including AquaHot. Rancho Santa Margarita owners bring coaches to Yorba Linda, where the furnace, its 12 volt supply and its LP supply are tested together. - Blower runs but no ignition usually means the sail switch never closed - Weak batteries cause furnace faults far more often than owners expect - Repeated limit switch trips point at blocked ducting - Hydronic systems are a separate skill set from forced air furnaces ### Key facts | Item | Value | | --- | --- | | Price range | $350 to $8,500+ (2 to 35 labor hours at $260 per hour) | | Labor rate | $260 per hour (Mechanical and electrical department) | | Typical turnaround | 2 to 10 shop days (Hydronic system work drives the long end) | | Written estimate | $150 (Credited in full against an authorized repair) | | Systems serviced | Suburban NT, Dometic and Atwood forced air, Truma Combi, AquaHot, Webasto, Espar | | Hazmat and disposal | $45 flat (Applies on jobs that open the LP or diesel fuel system) | Heat in a coach comes from one of three architectures and they have almost nothing in common. A forced air LP furnace pushes combustion heat through ducting. A Truma Combi makes space heat and domestic hot water from one compact unit. A hydronic system such as AquaHot burns diesel or runs an electric element to heat a coolant loop, then distributes that heat through exchangers in zones around the coach. Diagnosing one of these with habits learned on another wastes days. What they share is a dependence on the systems around them. A furnace that will not light is often a 12 volt problem rather than a gas problem, because the blower has to reach full speed before the sequence continues. A hydronic system that will not fire is often a fuel pickup or a burner screen loaded with carbon. We test the supporting systems as part of the diagnosis rather than after the parts fail to fix it. ## Three heating architectures, three different repairs Forced air LP furnaces are the most common by a wide margin. A Suburban NT or an equivalent Dometic unit pulls combustion air from outside, burns propane in a sealed heat exchanger, and pushes cabin air across that exchanger into ducting. The cabin air and the combustion air never mix, which is the whole safety premise, and it is why a cracked heat exchanger is a serious finding rather than an efficiency note. A Truma Combi does space heat and domestic hot water in one unit and it reports faults through a control panel with codes, which changes diagnosis into a mix of code reading and physical testing. A hydronic system such as AquaHot is closer to a small boiler: a diesel burner or an electric element heats coolant, pumps circulate it, and heat exchangers with fans deliver it in zones. When a hydronic coach loses heat in one bedroom only, the burner is almost certainly fine and a pump is not. - Forced air LP: Suburban NT, Dometic, Atwood, duct distributed - Combination: Truma Combi, space heat and hot water in one unit - Hydronic: AquaHot and Oasis, coolant loop with zoned exchangers - Diesel burners: Webasto and Espar, glow pin and burner screen service ## The ignition sequence and where it stops A forced air furnace does not simply light when the thermostat calls. It runs a sequence: the thermostat closes, the blower starts, the blower reaches enough speed to push a small vane called the sail switch closed, the sail switch tells the board that air is actually moving, the board opens the gas valve and sparks the electrode, and the flame sense circuit confirms combustion. Each of those is a permission and the furnace stops at the first one it cannot get. This is why the complaint owners report most often, a blower that runs with no heat, is so informative. The blower running means the thermostat and the motor are fine. No ignition attempt at all means the board never got past the sail switch. Three attempts and a lockout means the board got past the sail switch and never saw flame, which moves the investigation to the electrode, the valve and the gas supply. 1. Thermostat closes and calls for heat 2. Blower motor starts and comes up to speed 3. Sail switch closes on proven airflow 4. Board opens the gas valve and energizes the electrode 5. Flame sense confirms combustion and the cycle continues ## Why a weak battery bank looks exactly like a broken furnace Furnace blowers draw meaningfully on the 12 volt system, and a bank that reads fine at rest can sag hard the moment the motor spins up. When it does, the blower turns slower, the sail switch does not quite close, and the sequence stops. From inside the coach that is indistinguishable from a failed switch or a dead board, and it is why we measure voltage at the furnace terminals with the blower running rather than at the battery posts with everything off. Aging gel and AGM banks are the usual context. They hold surface voltage well and collapse under load, which makes them very good at fooling a resting voltmeter. Coaches that spend months in a storage lot between trips are the classic case: the bank has been slowly cycling down for a season, the first cold night of the trip is when the furnace is finally asked to work, and the owner concludes the furnace died in storage. ## Hydronic systems and what they actually need A diesel fired hydronic system carries maintenance obligations that a forced air furnace does not. The burner screen accumulates carbon and needs periodic service. The glow pin is a consumable. The fuel metering pump has a service life. Coolant needs to be the right chemistry and needs to be changed. Owners who bought a used diesel coach with an AquaHot rarely receive any of that history, and the first symptom of years of skipped service is a burner that lights hard, smokes, or refuses altogether. Zone distribution is the other half. Each area of the coach has a heat exchanger with a fan, fed by circulating pumps. A single seized pump or an air lock in the loop takes out a section of the coach while everything else works normally. That pattern, hot water available and one zone cold, is diagnostic on its own and it saves an enormous amount of time when the owner reports it accurately. > **warning:** Hydronic burner service intervals are not suggestions. A carbon loaded burner screen left in place accelerates its own failure and takes more expensive components with it. ## What heating system repair costs Work bills at $260 per hour from the mechanical and electrical department, across a range of $350 to $8,500 and higher on large hydronic overhauls. A sail switch, a blower clean and a multi cycle verification sits at the bottom. Board, valve and electrode work with duct correction sits in the middle. A full hydronic burner and zone system service on a forty five foot diesel coach reaches the top and can pass it. Parts carry standard markup, sales tax applies to parts and materials, and labor is not taxed. A $45 hazmat and disposal charge applies to jobs that open the LP or diesel fuel system. Jobs over $2,000 take a 50 percent deposit at authorization. The $150 written estimate is credited in full against an authorized repair. ## The coaches that need this most Southern California owners heat less than owners elsewhere, and that is precisely the problem. A furnace that runs three weekends a year sits idle long enough for the blower wheel to load with dust and for something to build a nest in the exhaust. The failures we see are storage failures far more often than wear failures, and they surface on the first genuinely cold night at elevation rather than at home. Full time owners and anyone chasing winter into the Sierra or the high desert run at the opposite extreme. Those coaches see real duty cycles, real duct wear and, on the diesel pushers, real hydronic maintenance intervals coming due on schedule rather than by surprise. ## Heat exchangers, exhaust and carbon monoxide The sealed heat exchanger is what keeps combustion products out of the cabin, and it is the one finding on a furnace that ends the conversation about repair. A cracked exchanger means the unit is replaced. There is no patch, no weld and no acceptable monitoring plan. We inspect the exchanger on every furnace that comes apart and we document what we find either way. Exhaust and combustion air routing matters just as much. A blocked exhaust tube, a nest in the intake, or a previous repair that left the concentric vent misassembled all push combustion products where they do not belong. If your coach has a carbon monoxide alarm that has gone off even once, treat that as the priority complaint and say so at intake rather than mentioning it in passing. ## Cost $350 to $8,500+, based on 2 to 35 labor hours at $260 per hour. Written repair estimate is $150, credited in full against an authorized repair. All work is performed in shop. ## Questions and answers ### Why does my RV furnace blow air but never produce heat? The ignition sequence stopped at the sail switch. The blower must move enough air to close that switch before the board will open the gas valve. A dust loaded blower wheel, a tired motor or a battery bank sagging under load all prevent that. We measure voltage at the furnace with the blower running to separate the three. ### What makes an RV furnace light and shut off every few minutes? The limit switch is protecting a heat exchanger that is running too hot, which almost always means air is not leaving fast enough. Crushed ducting, a disconnected duct boot behind cabinetry, or too many closed registers are the usual causes. Fixing the airflow stops the cycling. Replacing the switch alone does not. ### Why is one room in my coach always cold when the furnace runs? On a forced air coach it is normally a duct that has come apart or been crushed behind cabinetry, so the heat is being delivered into a wall cavity instead of the room. On a hydronic coach the same symptom usually means a seized zone pump or an air lock in that section of the loop. ### Can a weak battery really stop my furnace from lighting? Yes, and it is one of the most common causes we find. The blower draws hard on the 12 volt system, and an aging gel or AGM bank that reads fine at rest can collapse under that load. The blower turns slowly, the sail switch never closes, and the furnace never asks for gas at all. ### How often does an AquaHot system need service? The diesel burner side carries real maintenance intervals: burner screen cleaning, glow pin inspection, fuel filter and coolant service. Owners who buy a used coach almost never receive that history. We inspect the burner assembly and coolant condition at diagnosis so the actual state of the system is documented rather than guessed at. ### Can a cracked RV furnace heat exchanger be repaired? No. The sealed exchanger is the barrier between combustion products and the air you breathe in the coach, and a crack in it means the furnace is replaced rather than repaired. There is no weld, patch or sealant that is acceptable there. We inspect the exchanger whenever a furnace is opened and document the finding either way. --- Source: [OCRV Center](https://ocrv.me/services/appliance-repair/furnace-and-heating-system-repair/). Last verified 2026-07-29.