Raypak R185 / R265 / R335 / R405 Millivolt Heater: Pilot, Burner Tray, Header and Heat Exchanger Service

A Raypak millivolt heater has no display, no board and no error code. It has a standing pilot, a thermopile that makes a fraction of a volt, and a loop of switches that either lets that voltage reach the gas valve or does not. That is why the R185, R265, R335 and R405 from the RP2100 years, and the millivolt versions of the 185A–405B Versa series that came after them, are still running on so many pads: there is very little in them that cannot be fixed on the spot.

This guide is for the standing-pilot machines only. The digital IID versions of the same cabinets — the ones with a control panel and a spark igniter — are a different diagnostic and get their own article. If your heater has a lighter tube through the front and a thermostat knob instead of buttons, you are in the right place.

Which heater you have

The R185 / R265 / R335 / R405 numbers are the RP2100 family built roughly from 1993 to 1998. The number is the input in thousands of BTU. The 185A / 265A / 335A / 405A and the later B suffix are the Versa-era cabinets; each was sold as a millivolt unit or as an IID unit, and the parts differ between the two. Read the rating plate before ordering anything: the same tube bundle number can serve several inputs, but burner trays, refractory and headers are sized to one.

Parts on the model pages for the R185, R265, R335 and R405 cover the RP2100 series; the 185A, 265A, 335A and 405A pages cover the Versa cabinets.

Prep and safety

Shut the manual gas valve upstream of the heater and turn the gas valve knob to OFF. Kill any line voltage feeding an optional blower or remote. A millivolt heater does not need mains power to run, so "the breaker is off" proves less than it does on a digital unit — the pilot may still be lit. Let the heater cool before opening the top; the refractory holds heat for a long time.

Before you open anything, do the pad check. Pump running and primed, filter within its clean baseline, heater-loop valves open, pool at a sensible level. A millivolt heater proves flow through its pressure switch exactly the way a digital one does; it just cannot tell you that it did not.

The pilot: won't light, won't stay lit, lit but no main burner

The millivolt circuit is one loop. The thermopile sitting in the pilot flame generates a few hundred millivolts. That current runs through the on/off switch, the thermostat, the high-limit switches, the pressure switch and the fusible link, and returns to the gas valve coil. If every contact is closed, the main valve opens. If any one is open, the pilot stays lit and the burners never fire. Work it in that order.

Pilot will not light. Gas at the meter and at the heater, air bled from a line that has been off for the season, and a pilot orifice that is not packed with rust or a spider. If the pilot lights with a match but not from the lighter tube, the tube is misaligned or blocked, not the gas.

Pilot will not stay lit. The flame has to wrap the thermopile, not lick the side of it. Check that the pilot hood is clean and the thermopile is positioned in the flame, then check the two wire connections at the valve for corrosion. Only then put a meter on it, set to millivolts. Service literature and the field guides agree on the numbers: a healthy thermopile reads roughly 500–750 mV with the pilot lit and the circuit open, and the gas valve needs on the order of 250 mV to hold. A reading that looks fine open-circuit but collapses when the thermostat calls is a tired thermopile; a reading that stays high while the burners still do not fire means the problem is downstream in the switch loop, not in the pilot.

Pilot lit, burners will not fire. Jump nothing. Meter across each switch in the loop in turn — thermostat, high limits, pressure switch, fusible link — until you find the one that is open, then find out why it is open. A pressure switch open with the pump running is a flow problem or a scaled exchanger before it is a bad switch. A high limit open is the exchanger telling you the same thing (see the governor section below). A fusible link that has parted has seen a real over-temperature in the combustion chamber.

Every component in that loop — pilot assembly, thermopile, gas valve, thermostat, high limits, pressure switch, fusible link — is part of the appliance's gas train or its safety interlock, and it is OEM-only. We wrote about why that boundary is where it is. What is ours around the pilot is the metalwork that holds it: the 305161F standing-pilot mounting bracket for the 185A–335A millivolt units and the 306693 bracket for the 185B–335B millivolt units, plus the 62996 lighter tube. A pilot that will not light from the front is very often a bracket that has rusted through and let the assembly droop away from the lighter tube.

The burner tray: rust, soot and burners that will not sit

Slide the burner tray out (it comes forward once the manifold union and the pilot lines are off) and look before you clean. Three things show up on a tray, and each one says something different about the heater.

Light surface rust is age. The tray is steel in a damp cabinet; it will rust.

Heavy black soot on the burners and the underside of the exchanger is condensation. Combustion gases condensing on a cold exchanger produce carbonic acid, which drips onto the burners and, over time, eats the copper fins. On a Raypak this almost always traces back to the Unitherm governor (below) letting the exchanger run too cold. Cleaning the burners without fixing the governor buys you one season.

Burners that rock, sit crooked or have fallen off their spacers are a hold-down problem, and they will burn with a ragged flame that soots the exchanger even when the governor is fine.

The tray itself is a normal aftermarket part when the steel has rusted through or the burner ports have distorted. It is supplied without burners and without the manifold: the 005265F for the R185, 005266F for the R265, 005267F for the R335 and 005268F for the R405. Your burners, manifold, orifices and gas valve transfer across; if any of those need replacing, that is OEM work.

Renew the burner spacer and hold-down kit whenever the tray is out — 005237F for the R185, 005238F for the R265, 005239F for the R335 and 005240F for the R405 — so the burners go back at the correct spacing under the exchanger.

While the tray is out you are looking at the refractory. Cracked or crumbling firebrick lets flame reach the cabinet and is a cause of parted fusible links. Left and right panels are 005282F; front and rear panels are model-specific (005284F R265, 005285F R335, 005286F R405), held by the retainer kits 005287F through 005290F. The 005283F front and rear fire block is the R185's equivalent.

Headers and gaskets: where the water shows up

Water on the cabinet floor comes from one of three places, and it is worth ten minutes to establish which before parts are ordered.

At a flange. A weep at the inlet/outlet flange or the return flange is a gasket: 800080B for the 2-inch flange, 062236B for the 1-1/2-inch. Renew the bolt kit at the same time (001303F for the 181–403 cabinets, 006712F for the R185–R405); rusted bolts are the usual reason the gasket was not compressed evenly in the first place, and they are also why the header does not come off cleanly the next time.

At the header itself. A cast iron header that has corroded through, or one whose gasket face is pitted beyond sealing, is replaced as a unit. The inlet/outlet header is 003759F in cast iron or 003760F in bronze for the 185A–405B cabinets and the R185–R405; the return header is 002450F in cast iron or 002451F in brass. Match the material to what came off unless the water chemistry history argues for the upgrade. Between the header and the tube ends sits a set of small flat gaskets, one per tube — the 800014B nine-pack. Replace all of them; reusing one compressed gasket in a set of nine is how a rebuilt exchanger comes back with a new leak.

At the tubes. A pinhole in a copper tube leaves a greenish stain where chlorinated water has oxidised on the fins, and it shows up as a drip that follows the fin pack rather than a flange. That is a tube bundle, and it takes you to the next section.

The 005264F rear drain plug and cover, the 005393F CPVC adapter kit and the 005302F side panel cap round out the water-side hardware that is worth having on the truck when a header comes off.

The heat exchanger and the Unitherm governor

The Unitherm governor is a wax-element thermostatic valve in the header that bypasses part of the return flow until the exchanger is warm. Its job is to hold the exchanger at roughly 105–115°F regardless of pump flow and pool temperature, because below about 100°F combustion gases condense on the copper. Sources on both the service and the retail side agree on the failure picture: a governor stuck open runs the exchanger cold — condensation, carbonic acid, soot on the burners, a rusted cabinet floor; a governor stuck closed starves the exchanger — localised overheating, scale, high-limit trips, and a whistling or whining sound on start-up.

Pull it and inspect it. The element should be free on its spring with no scale binding it; some technicians drop it in 120°F water to watch it open. When the governor is a corroded mess, the bypass behind it usually is too. The 062234B governor fits the R185 through R405, with the 850254 retainer spring; on the polymer-header A and B units the equivalent is the 006719F, with the 006720F plug and the 062235B bypass valve and 850253 bypass spring.

The exchanger itself is a finned copper tube bundle. Scaled tubes from years of low flow or hard water can sometimes be acid-flushed once, but a bundle that has been sooted and acid-etched from underneath, or that is weeping at a tube, is a replacement. Match by model: 005252F for the R185, 005253F for the R265, 005254F for the R335 and 005255F for the R405 in the RP2100 series; 004671F through 004674F for the 183–403 Versa cabinets. Fit the model's baffle kit into the new tubes (005260F R185, 005261F R265, 005262F R335, 005263F R405) — without baffles the water short-circuits down the centre of each tube and the bundle runs hot.

Two rules that both the field guides and the repair trade repeat. First, replace the governor with the bundle, every time; a new bundle behind a failed governor sooths up within a season. Second, know when to stop. If the header faces, the burner tray, the refractory and the cabinet floor are all gone, the heater is a chassis with a new exchanger in it, and the customer is better served by a replacement unit.

What is aftermarket work and what is OEM-only

OEM-only: gas valve, pilot assembly and thermopile, pilot orifice, burners and burner orifices, manifold, thermostat, high-limit switches, pressure switch, fusible link, pressure relief valve. Everything that meters gas or exists to shut the heater down when something has gone wrong.

Aftermarket work: tube bundle and baffles, Unitherm governor, bypass valve and springs, inlet/outlet and return headers, flat and flange gaskets, bolt kits, burner tray (without burners), burner spacer and hold-down kits, refractory and retainers, pilot mounting bracket, lighter tube, drain plug, jacket tops 005303F and 005305F, indoor stack kits 6696 / 6697 / 6698, and the thermostat knob 009499F. These are structural, sealing and flow components. They rust, scale and crack; replacing them does not change how the heater lights or how it shuts itself down.

Cross-reference table

Sourcing

POOLPOINT manufactures the structural, sealing and flow components above factory direct for US distributors, service companies and online sellers. MOQ starts at 50 pieces per SKU, mixed cartons are accepted to reach it, and private label is available. We do not supply gas valves, pilot assemblies, thermopiles, burners or any safety switch for these heaters, and will tell you so if asked. Request a quote for wholesale pricing on the parts we do make.