Maintenance, Cleaning, and Trouble Shooting

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 recommend 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 down sizing 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 in side 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.



Here is where you start:


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 water jacket.  There are two ways to do this.  With the Heat Wise burner you can also remove the burner and slip the vacuum hose in the hole and stuff a rag around it.  The vacuum will pull the debris 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 need to be brushed and vacuumed also.

Caution:  The top baffle has a rock wool insulator.  A vacuum will destroy this piece before you can react.  I recommend just banging is a bit to shake loose 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 tap it off with a small hammer.  On replacing it dab some Teflon pipe dope or other anti-seize product on the boiler surface.

The following pictures show the sequence of events:

(more to come)






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.  If 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 one here.  If the boiler has sooted, and, the drain from the condenser is plugged and you flush the condenser without doing this you will have water/soot mix all over the floor.  Clean if necessary.

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.

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 shut down.  Cleaning a sooted boiler is a fate worse than death.  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 if the surface through sustained condensing.  Some of the reasons that this can happen is very large homes, with high mass heating devices, set back thermostats, high setting on the mixing valve.  Anything that drags the boiler core temperature down for significant periods can cause this to happen.

Here is what to look for:  On removal of the bottom baffle (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.  Currently there is no ASME certification required.  Note, I have only seen this twice, once in an overly large house, and once in a person who put third party temperature controls on and was running the boiler too cold.  Please note that this problem is common to ALL boilers that are sized properly to the residense.  In the past boilers were sized 3 to 4 times larger than needed and it never occured.  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 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.  I have cleaned some up put a slight layer of silicon seal on some to see if that helps.  Caution should be used as you do not want to insulate the probe.

Venting Issue

If you purchased your boiler before 2012, you most likely have the Monitor FCX 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 replacement.  Pictures

Back Drafting

Negative pressures and variable pressures and air flows 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.



Burner Cleaning

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



Discussion on Tuning

All things being properly assembled and cleaned, the boiler burner’s has only two variables for any given nozzle size.  This is the fuel pressure and the air volume adjustment.  All of 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.  Various methods exist for reaching the proper specifications, some being more easily used and reliable than others.  First of all, let’s dispense with the idea that you can optimally adjust this boiler by sight – it is not possible.

Another option consists of a trial & error method of chemically measuring CO2 and using temperature readings and charts to calculate excess air, and O2 based on fuel type.  This method has been used for years, but the drawback is that minor adjustments in air, combined with the margin for error in the chemical and human process can create significant variations in readings.

The best method for tuning any boiler is using an electronic flue gas analyzer such as a Bacharach.  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

It should be noted that adjusting the boiler with an electronic stack analyzer is the only way to measure the efficiency of condensing.  And not all of these devices do this.  An understanding of how this works is useful and one should take efficiency readings on condensing boilers with a grain of salt.

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 a guess because stack temperature does not create condensing, only lowering the flue gas temperatures with the return water.  So this means that a 150 degree or for that matter, a 200 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.

So consider the tuner a relative device.  Actual efficiencies are determined in the lab.  These devices are used to tune the boiler to the optimum burn efficiency and they do not measure total efficiency for a condensing boiler.  See the discussion on efficiencies in the Overview section.


Burner Adjustment

CAD cell can be checked using an ohmmeter or many controllers have a self-diagnostic routine.


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.  This puts you on the top edge of the CO2 level and the highest efficiency, and minimum air needed.  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.


Boiler Faults

The details in this section pertain primarily to the Heat Wise burners, but the principles are the same for the Riello

How the Honeywell Controller Works

The normal sequence of events is:

  1. On a call for heat the heater imbedded in the nozzle turns on.
  2. When the temperature of fuel in the nozzle is 130 F the blower turns on and the electrodes begin firing.
  3. The cad cell must not see light.
  4. The burner runs 15 seconds (the pre-purge) to get the air moving up the stack.
  5. If the cad cell sees light before the pre-purge is done it shuts down.
  6. The solenoid opens providing fuel and is ignited.
  7. If the fuel is not ignited the cad cell senses no flame and it shuts down.
  8. Once the cad cell senses the flame the electrodes turn off after about 5 seconds

Burner Shutdown - Honeywell Controller Light flashing and Top Red Light is on

This means you have a flameout.  You can push the reset button twice.  If the boiler does not start and run properly in two tries the controller goes into lockout.  You can remove the lockout by holding the button down for approx 45 seconds and this resets it to two more tries.  However, if it does not run properly after two tries you probably have more serious problems.  The lockout is there as a safety.  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 detuning 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 spark, fuel, air, or controller problem.


Stack Over Temperature

Note the reset button does not pop out.  Use a toothpick or other pointy device to reset, it will click if it has tripped.  You have a serious detuning 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.


Water Over Temperature

Note the reset button does not pop out.  Use a toothpick or other pointy device to reset, it will click if it has tripped.  Probable causes are malfunction of the aquastat temperature control or malfunction of the over temperature safety.  Running the boiler at too hot a temperature.  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 is an anomaly that does not happen all the time.  Reducing the boiler temperature solves the problem.  If you have to run the boiler hot then you may need to provide for purging the boiler to a zone or the domestic loop when there is no call for heat.

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 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.


The boiler “woofs” on firing

Then Starts and burns smoothly

The most common cause of this is a small amount fuel is leaking into the burn chamber during the pre-purge on startup or after the burn cycle is completed.  Given that the boiler is in tune, getting proper fuel, etc., the most probable cause is a faulty solenoid valve.  Depending on the severity of the leak it can just be an annoyance that does not affect the running of the boiler or it can actually shut down the boiler from the disruption of the burn causing the CAD cell not to recognize the flame.  Note that boiler shutdown can be intermittent.

Fires Without Pre-Purge and Then Flames Out

This also can be the malfunction of the solenoid valve.  It maybe stuck partially open.  The way the Honey controller works is that the burner will not fire if the cad cell sees light on startup.  Also if it sees light before the pre-purge finishes it will shut down.  It can also be a bad controller.


Startup seems normal then lots of smoke

There is probably a fuel leak inside the burner.  It may be a loose or cross-threaded connection at the nozzle assembly, a loose nozzle, or the two pieces of the nozzle assembly that is sealed by an o-ring may be leaking.  Boilers have seemingly run fine for years and this happens, but it usually happens within several days of startup.

Leaking Fuel

This leaking can also manifest itself in fuel pooling in the burner and leaking out.  The burner may appear to be burning correctly.


Flutter (uneven burn) and flame out

This is common at startup when the air is not properly adjusted.  This is usually too much excess air and you are blowing the flame out.  This can also result in blowing too much heat through the boiler and causing an over stack temperature shutdown.