Frequently Asked Questions

A number of frequently asked questions are provided here for your convenience.  For further information or clarification, please contact the A.O. Smith Water Heaters technical department.

Standing Losses for AO Smith Gas Fired Water Heaters

The below table shows standing loss data for the Innovo and BFC Cyclone ranges of water heaters.

Please beware that these values should not be entered into a Part L calculation such as SBEM. SBEM asks specifically for the standing losses from a hot water storage tank.  A direct fired water heater is not a hot water storage tank.  The standing losses from a water heater are accounted for in the BS EN 89 efficiency calculation, which is considered a seasonal efficiency, and is entered into the SBEM software.  Therefore, if you enter the standing losses into the software as well, you are effectively doubling the losses (by including them in both the seasonal efficiency and in the standing losses entry box), and with double losses, the installation is likely to fail. If you must put details of the tank into the calculation, then you should put the insulation type and thickness (Polyurethane foam, 50mm, 0.023 W/m*K).

Below is an extract from the non-domestic building services compliance guide to prove the above statement.

Standing losses for BFC and IR water heaters:

Appliance Model

Standing Losses (kWh)

According to EN 89
Innovo Water Heaters
IR 12-160 2.16
IR 20-160 2.16
IR 12-200 2.30
IR 20-200 2.30
IR 24-245 2.64
IR 32-245 2.64
IR 24-285 2.98
IR 32-285 2.98
IR 32-380 2.90
BFC and SGS Water Heaters – Generation 3
BFC 28 / SGS 28 4.20
BFC 30 / SGS 30 4.70
BFC 50 / SGS 50 4.70
BFC 60 / SGS 60 4.70
BFC 80 / SGS 80 6.70
BFC 100 / SGS 100 6.70
BFC 120 / SGS 120 6.70

Using Water Softeners

The use of a water softener, magnetic or otherwise, should not pose a problem to a domestic hot water system so long as the resulting water is not softened beyond a minimum hardness level of 100 ppm.  Reducing the hardness below this level may result in damage to the water heater and domestic hot water system.  It is advisable to blend softened and non-softened water together until the resulting hardness is 100 ppm or higher.

Please be advised that the use of water softeners does not eliminate the need for regular servicing of water heaters, but may reduce the required frequency—for example, increasing the service interval from every six months to annually.  A suitable service interval should be determined by a qualified engineer upon examination of the installation.

BFC Cyclone and IR (Innovo): Required Flue Fall

The BFC Cylcone and IR (Innovo) condensing gas water heaters require a minimum of 5 mm fall for every 1 m flue length

BFC Cylcone and IR (Innovo): Controller Differences

Both the BFC Cyclone and IR (Innovo) water heaters feature integrated controllers, however there are a number of differences between them:

BFC Controllers:

  • Display up to three lines of text, sequence, and fault messages together with the current appliance status and time
  • The menu key, stylized as a book, can be used to access the menu, set time programmes, change the time, and change the set point temperature
  • The service menu key, stylized as a spanner, can be used to change the hysteresis, view the appliance and fault history, set high/low fire for flue gas analysis, and set a number of other functions including anti-legionella purge to allow a higher set-point temperature for a period of one hour.  This menu can also be used to reset the service interval reminder (see FAQ’s below)
  • The appliance can be controlled either by its own time clock or by external BMS

IR Innovo:

  • Displays up to three characters (code) together with a further 7 status symbols around the edge
  • The menu key, stylized as a book, can be used to access the menu and display all 32 parameters as either a three digit number or abbreviated message.  The values of parameters can be determined and adjusted using the arrow and enter keys
  • The appliance does not feature a built-in timeclock, however can be controlled by BMS
  • The appliance does not feature a legionella purge function
  • The service reminder can be turned off if so desired

IR (Innovo): Required Clearances

The IR (Innovo) range of water heaters requires the following minimum clearances for service and access:

  • Above: 300 mm
  • Rear: None
  • Side: 200 mm on each side
  • Front: 1000 mm

BFC Cyclone: Maximum Burning Hours Reset Procedure

To reset the maximum burning hours of an A.O. Smith BFC Cyclone water heater, begin by identifying the generation of the appliance.  This can be done using the serial number found on the appliance data plate.  Generation III units have a serial number starting 0938 and higher.  Generation II and older units will begin with serial numbers starting 0937 and lower.

Next, press the spanner key on the appliance display board to enter the Service Menu. Use the Up and Down arrow keys to highlight the ‘Service Interval’ menu option, and press the Enter key.  Use the Up and Down arrow keys to highlight the desired service periodicity.  The default option is 12 months.

For Generation III appliances, press and hold the Reset and Enter keys simultaneously, holding for 10-15 seconds until the display goes blank.  The buttons must be pressed at exactly the same time; if the display immediately reverts to an earlier menu screen upon pressing both buttons, please re-navigate and try again.

For Generation II appliances, press and release the Reset button, followed by the Enter button.

Following this procedure, the appliance maximum burning hours will be reset.

BFC Cyclone: Maximum Working Pressures and Higher Pressure Safety Valves

The BFC Cyclone data badge states a maximum working pressure of 5.5 bar, however in some installations you may find it supplied or installed with a safety valve set at a higher pressure.

The reason for this is due to the WRAS approval of the BFC water heater.  The true design operating pressure of the BFC range is 8 bar working (test pressure 12 bar) in line with BS EN 89, and there is no issue operating the appliances at these pressures.  However, during the WRAS approval process, the water heater was approved alongside an unvented kit featuring the most common and economical unvented components.  One of these ancillary components was a pressure reducing valve with a variable pressure range from 1 – 5.5 bar.  This is the pressure figure that is represented on the BFC data badge, and is suitable for most applications.

For high pressure installations exceeding 5.5 bar, the BFC must be paired with different unvented components.  The water heater still meets the requirements of WRAS so long as these components are also WRAS approved parts.

According to BS 8558, the pressure relief valve and T&P relief valve set pressure sshould be set to 0.5 – 1.5 bar above the maximum working pressure of the tank.  It is good practice to set the pressure relief valve to a lower pressure than the T&P relief valve, because T&P valves are more likely to improperly re-seat after opening.  The pressure relief valve therefore protects the T&P.

Therefore, the maximum pressures advised for an 8 bar BFC installation would be 8.5 bar for the pressure relief valve and 9.5 bar for the T&P relief.  However, as these are special order components, they are typically set according to the best settings based on the site requirements, so often are not quite this high.

BFC Cyclone: How to Set the Controller Day and Time

  1. Press the menu button
  2. Scroll to SETTINGS
  3. Select DAY/TIME
  4. Choose the day
  5. Set the time

BFC Cyclone: Controlling Water Heaters Through BMS with Anti-Legionella Programme

The BFC Cyclone water heater operates in one of the 4 below modes:

  • “ON”, where the water heater is in continuous operation
  • “OFF”, where the water heater is in a standby state.  Note that the appliance is still electrically live in this state.
  • “WEEK PROGRAM”, where the water heater will run according to a schedule which will define daily operation and standby periods throughout the week
  • “EXTERNAL ON”, which will allow an external override by closing terminals 21/22 to turn on the water heater

It is therefore possible to have one of the following scenarios:

  • 21/22 are closed, and the water heater is in operation
  • 21/22 are open, the water heater is in the “ON” mode, and is in operation
  • 21/22 are open, the mode is “WEEK PROGRAM”, and the water heater is operating according to the selected times in the week program schedule
  • 21/22 are open, the mode is “WEEK PROGRAM”, and the water heater is in standby according to the selected times in the week program schedule
  • 21/22 are open, the mode is “OFF”, and the water heater is in standby

Anti-legionella is a function of the week program, and will turn on the appliance at a set time once per week.  To activate the anti-legionella function the water heater must be set to “WEEK PROGRAM” mode.  Within this mode, the water heater can be selected to be always in standby – which will allow the appliance to then be controlled through the BMS by opening/closing the 21/22 terminals.  The anti-legionella function will override the 21/22 terminals once per week to run the legionella purge (with the consideration of using a destratification pump).  Note that a fire alarm will also stop the operation of the water heater using the 21/22 terminals, as well as independently closing the mains gas supply.

However, if the anti-legionella cycle needs to run daily instead of weekly, the settings will need to differ.  Configure the “WEEK PROGRAM” mode to have the water heater operating for 2 hours per day (e.g. run during 2am – 4am, and on standby for the rest of the day).  During these two hours the WEEK PROGRAM schedule will activate the water heater regardless of the 21/22 terminal state, overruling the BMS to allow the anti-legionella cycle to proceed.  At the end of the cycle the water heater WEEK PROGRAM will set the water heater back to standby, whereupon the BMS regains control through the 21/22 terminals.

BFC Cyclone: Burner Diffuser Plate Cracking on Generation I and Generation II Units

BFC Cyclone models 28, 30, 50, and 60 within the first and second generation feature a burner diffuser plate at the bottom end of the burner assembly.  This plate contains a number of holes punched through the material and is shaped to produce an optimal, cyclonic flame pattern to maximize heat transfer from the burner.  The manufacture of this diffuser plate creates material stress on the locations of the bends and punches.

As soon as the appliance is used, the burner plate is likely to experience cracks in this stressed locations.  This cracking of the material is a known consequence of standard operation, and may occur on a short timescale dependent upon the intensity of the appliance usage.  The cracking cannot be prevented.  Furthermore, the cracking relieves the material stress present upon the diffuser plate and imparts no negative consequences upon the operation, efficiency, performance or lifetime of the burner assembly or water heater.

Since the introduction of this burner plate in 1998, A.O. Smith Water Heaters have experienced no failures, negative consequences, or negative feedback arising from a cracked burner diffuser plate.  These construction of these plates and appliances have been thoroughly tested.

Changing the diffuser plate or attempting repairs, such as by welding, will not solve the cracking and may in turn incur a negative influence upon the water heater due to the potential for changes in the flame pattern.  Replacing a cracked burner plate is not recommended due to the likelihood of recurrence after a short time.