As of December 2019 the FCX will no longer be available in the U.S.



Maintenance, Cleaning, and Trouble Shooting – Revised 2019

While there may be some things new to the professional, I am attempting to provide a basic understanding of how things work to the individual owner.  Being a mechanic type in another field will help put the basics together much faster.  Having no knowledge of anything mechanical hopefully this will provide a beginning.


It is recommended that the boiler be serviced at every 1000 gallons of fuel usage or at a minimum of once a year.  Servicing consists of not only cleaning, replacement of the nozzle and other parts, but a thorough inspection of all facets of the boiler system.  The cleaning of the boiler and replacement of the nozzle is quite simple and can be accomplished by nearly anyone as described in the following.  Not only is the procedure simple, it requires no special tools, and will save you money.  The actual tuning of the boiler requires professional equipment.  This is not something that can be done by eye as has been common on older boilers even for professionals.  Why do we need to do this?  Well consider The FCX as the Ferrari of boilers.  If you had a Ferrari would you: change the oil? keep it clean? tune it up? Here are some other reasons why past practices have differed.

There currently is a tendency industry wide to use smaller boilers.  There are several reasons for this.  Houses are being better insulated which requires less heat, but the biggest reason is that over-sizing boilers is inefficient, both in initial cost and in operating costs.  So, while it has been proven that downsizing to a smaller boiler that runs more frequently can considerably increase efficiency and reduce standby costs, the reduced physical size of the boiler will require cleaning more frequently.  (The burning of fuel leaves deposits of unburned debris inside the boiler.)  In the past, it is not uncommon for the oversized boiler to go several years or more between cleanings.  The reason is they are larger in volume (holds more debris) and uses larger nozzles at lower pressures (less wear) and don’t run as often.  Some professional boiler technicians also believe there is a lot of variation in fuel quality.




Primary Heat Exchanger

After removing the baffles, the boiler jacket needs to be brushed down.  Insert a vacuum (a shop-vac type is best) to the bottom of the primary, or you can remove the burner and slip the vacuum hose in the hole and stuff a rag around it.  The vacuum will pull the debris and ash to the bottom.  If the burner has been operation properly, there will be no soot on the sides, a little ash, but mostly residue and debris from the unburnable minerals in the fuel.  The baffles (they are called swilers) need to be brushed and vacuumed also.  Note the FCX 22 has smooth sides and the FCX 30 has welded flutes so different brushes are needed.

Caution:  The top baffle has a rock wool insulator.  A vacuum will destroy this piece before you can react.  Just bang it a bit to shake loose and what you can.

Next remove the nut that holds the glass observation glass on.  If the glass sticks to the boiler, do not use a pliers to remove, it will break.  Take a small pocketknife and wedge/tap it off with a small hammer.  On replacing it, dab some Teflon pipe dope or other anti-seize product on the boiler surface of the port and you will never have another problem.


After cleaning the boiler, next is the condenser.  The condenser is skeleton fire tube type, where the flue gases pass through the tubes that are surrounded by water.  This boiler utilizes the counter flow method of heat transfer for both the primary heat exchanger and the secondary (condenser).  This means the flue gases flow in the opposite direction as the water through the boiler.  This is for two reasons.  First, it is the most efficient method of heat transfer, where the hottest gases heat the hottest water and the coolest gases heat the coolest water.  Secondly, with the gases moving down the tubes the condensate continuously flushes the tubes clean.

In a properly running boiler, when you open the condenser you will see a slight film of soot on the top of the condenser tubes.  This extends down the tubes about an inch.  From there the tubes will be shiny.  This is not the case if the boiler is not running in condensing mode.  I.E. the return water is not cool enough to promote condensing.

First, inspect the condensate drains, from the condenser and from the stack if there is a separate connection for draining the stack. 

Next, flush the condenser with water.  Generally, when in normal operation this will clean any particles from the condenser and brushing will not be necessary.  In certain cases you may have baked on carbon or if in construction, baked on sheetrock dust, paint, etc.  The absolutely worst is baked on varnish from lacquer overspray.  In this case you will probably have to use a side-grinder on the primary, lacquer thinner on the condenser, and q-tips on the fan.  The boiler will stink for weeks.  Combine any kind of paint overspray with the sheetrock dust and you have a substance that resembles concrete.

Caution! If the boiler has sooted, it is possible the drain from the condenser is plugged with soot also.   So when flushing observe the water level in the condenser by looking down one of the tubes.  The worst thing that has happened to me is the condenser filled with water/soot mix and flowed into the primary and then through the burner and on the floor.  It took half a day to cleanup.

On returning the cover, dab on some Teflon pipe dope or other anti-seize product on the gasket surface.  It will keep it from sticking.  Be sure not to pinch the gasket.

Non-Condensing Mode

If you must run in non-condensing mode for any length of time, depending on how often and how long you run you should flush the condenser more often.  If you do not, the condenser tubes will slowly plug, the boiler will de-tune, over heat, and the boiler will soot more and shut down.  Cleaning a sooted boiler is a pain.  Also, be sure you check the condensate paths more often.

Inspection of Primary, Secondary, and Venting

Primary Heat Exchanger

Here the primary concern is the deterioration of the surface through sustained condensing.  Some of the reasons that this can happen is very large homes, with high mass heating emitters, set back thermostats, high setting on the mixing valve and no boiler protection.  Anything that drags the boiler core temperature down for significant periods can cause this to happen. Also, a malfunctioning aquastat can caus this by running the system too cool.

Here is what to look for:  On removal of the bottom baffle FCX22 (it’s called the swirler), you will see a ring mark where the outer baffle touches the inside of the boiler water jacket.  This is normal, but after cleaning, if there is an indentation here you are probably condensing, as there is a slight leakage of flue gas here being cooled too much.  A good welder can repair this.  The current certification standard is U 723.  In the past I have only seen this twice, once in an overly large house (6,500 SF with setback thermostats), and once where a person who put third party temperature controls on and was running the boiler too cold.  However, it was found in time, and no repairs were necessary. Recently, a failure of the aquastat may have caused to problem and is under invsstigation. Please note that this problem is can occur to ALL boilers that are sized properly to the residence with out controls to prevent it.  In the past boilers were sized 3 to 4 times larger than needed and stayed hot all the time and it never occurred.  Also note, this can be prevented with proper controls and piping.

Secondary Heat Exchanger (Condenser)

Inspect the Drains as described above.  Only one problem has been found here and it is not the condenser itself.  On the front of the condenser (pre-2012) there is a plastic insert that is sealed by an O-ring.  It also contains a stainless well that holds the over stack temperature probe, and the port for inserting a flue gas analysis probe.  The well can deteriorate and allow condensate to reach the probe causing a shutdown.  On only one boiler has this happened but I have noticed pitting on several. 

Venting Issue

If you purchased your boiler before 2012, you have the Monitor FCX 20 boiler.  On these boilers, there have been some issues with part #2363.  This is the connecting piece between the condenser and the PP plastic stack.  This piece is a welded assembly of thin stainless steel that is not totally resistant to the slight acidic content of the condensate.  The time line of failure of this piece is not predictable.  So at least once a year you should check all venting and in particularly this piece.  On the new Geminox boilers this piece has been redesigned.  It is now an assembly with a PP plastic core and an outer steel enclosure. Contact your supplier about a free replacement.  Pictures

Back Drafting

Check for negative and variable pressures.  Air pressure differences can greatly affect the running of the boiler and should be avoided. See the Single Wall Side Exits and Negative Pressures under Installation Stacks & Venting.


The Burner

In 2012 Lucky Distributing acquired all rights and inventory from Monitor Corporation.  At this time, I became the Tech Rep and immediately pushed for a replacement of the Heat Wise burner. The overwhelming choice in burners was the Riello, and the series 40 burner was the most popular.  The FCX 22 and 30 were sent to the North American Riello testing lab.  They chose the RDB series of burners as the most adaptable to our needs.  It is extremely well designed.
The RDB has several advantages over the 40 Series:

From here on all references to burners will refer to the RDB as many the Heat Wise and Becket NX’s have been replaced.  On those that haven’t the servicer has most likely mastered their idiosyncrasies.

Burner Cleaning

The instructions that come with the burner need to be followed.  Here are the essentials that need to be examined:



All things being properly assembled and cleaned, the burner has only two variables for any given nozzle size.  This is the fuel pressure and the air volume adjustment.  All these settings and burn specifications are detailed in your burner and boiler manuals.

Any change in any of the two variables of fuel an air will affect the combustion.  Improper fuel pressure changes the amount the fuel is atomized and the combustion pattern.  And if a boiler is not cleaned, the accumulation of the debris affects the flow of air along with the air setting.  Too much air and you blow heat out the chimney, too little and you don’t get proper combustion.

All things now being properly set, and fuel pressure adjusted, tuning a boiler simply means adjusting the amount of air that feeds the combustion.  First, let’s dispense with the idea that you can optimally adjust this boiler by sight – it is not possible.

The best method for tuning any boiler is using an electronic flue gas analyzer such as a Bacharach or Testo.  This measures some components and calculates others such as efficiency.  A continuous readout during the entire burn cycle (startup to boiler at max temperature) can be accomplished and slight adjustments are immediately visible.  This is virtually impossible with any other method.

A smoke spot tester is also required and is the bottom line on tuning.  Regardless of any other settings, if your boiler is making smoke (free carbon) it is not tuned properly.

Electronic Readings

These devices measure directly stack temperature along with O2 and CO.  Based on the fuel type, it calculates CO2, excess air, and efficiency.  The devices that do add the efficiency from condensing based on these and an algorithm that that uses stack temperature and fuel type.  This is basically an indicator because stack temperature does not create condensing, only lowering the flue gas temperatures with the return water.  So this means that a 150 degree stack temperature could either be or not be condensing.  In fact, on the first stage of condensing, the overall flue gas temperatures do not have to be lowered at all.  The key here is that when the water part of the flue gas condenses, it does not change temperature while giving up the latent heat of vaporization. This happens when the water goes from the vapor state at 212 °F to the liquid state at 212 °F (no change in temperature).  The tuning device has no way of measuring this.  This is why the FCX easily attains an efficiency of 93%+ in radiant applications. The only real indicator of efficiency is how much fuel you use.

So consider the tuner a relative device.  Actual efficiencies cannot even be determined in the lab.  These devices are used to tune the boiler to the optimum burn efficiency and they do not really measure total efficiency.  See the discussion on efficiencies in the Overview section. Again, the only real indicator of efficiency is how much fuel you use.

Burner Adjustment

On initial startup the burner must be tuned.  The RDB burner is shipped separately from the FCX and needs adjusted. The fuel pressure us usually about 140 PSI. The air adjustment is such that it usually will run out of the box, but it will not be clean. The air setting is affected by length and type of stack. You will need professional equipment to properly set the CO2 and excess air levels.  Small changes of the air setting can change the efficiency by several percent. Air settings are lowered from maximum because the maximum leaves no margin error. The FCX runs well in most cases with even higher levels of CO2, however, conditions change, parts wear, etc, so the recommended settings give a margin for error. The following is what is recommended.


Old Timers Tuning

Assuming the burner is producing no smoke, with a smoke tester (cost about $100) gradually decrease the air until you get a trace of smoke.  Then increase the air to no smoke.  This puts you on the top edge of the CO2 level and the highest efficiency, and minimum air needed, but with no margin for error.  Check often and increase air as needed.  Set up a schedule for this.  Settings vary over time do to parts wear etc.  Best to have a little margin for error.



Burner Shutdown - Top Red Light is on

This means you have a flameout.  It is reset by the button on the burner. Some of the causes of a flameout are air in the fuel lines, failure, sooting or improper alignment of the CAD cell, worn nozzle producing incorrect burn, fuel pump pressure too low, cracked or misaligned electrodes, and de-tuning of the boiler.  Don’t forget, you may be out of fuel.  Examine top of de-aerator on start up for bubbles.  Check pump pressure.  Pumps can fail intermittently.  Check CAD cell for cleanliness and cell resistance (see the manual).

The bottom line - there is a cleanliness, adjustment, spark, fuel, air, or controller problem.

Water Over Temperature
Note the reset button does not pop out.  Listen for a when you do a reset.  

Running the boiler at too hot a temperature can cause this.  What happens here is that when there is no longer a call for heat and the zones close down, the boiler continues to heat up to its setting controlled by the aquastat.  If this is set too high the residual heat in the steel can over temperature the water.  This surge is an anomaly that happens all the time. The temperature always surges when pumps stop and burner is stopped.  Reducing the boiler temperature solves the problem. 

Also check the air eliminator at the back of the boiler.  The boiler does not purge itself of air if this is not installed.  This will cause an over water temperature fault as there is not enough water mass in the boiler to absorb the heat surge at normal shut off.

A faulty aquastat or faulty high water temperature safety can also cause this shutdown.  To check, there is a third temperature well in the boiler in which a thermometer can be place to monitor temperatures and determine what is happening.

Stack Over Temperature

Note the reset button does not pop out. .  If this has tripped you have a serious de-tuning problem.  This could mean a bad nozzle, dirty boiler, improperly tuned (too much excess air blowing the heat up the stack, blocked stack, etc.  Find the problem and fix it before running the boiler to any extent.  This is not caused by an anomaly and must be addressed.


Work in progress