CATALYSTS (continued)
In order to calculate the combustion ratio for the appliance (CO/CO2) it is first necessary to express
both gas concentrations in terms of percentage. To convert from parts per million (ppm) to a percent-
age (%) divide the ppm figure by 10,000. Examples : 35ppm = 0.0035%, 15ppm = 0.0015%, 5ppm
= 0.0005%.
Now divide the concentration of carbon monoxide (CO) expressed in percent by the concentration of
carbon dioxide (CO2) to obtain the appliance combustion ratio.
The combustion ratio of the gasses emitted by the catalytic convertor should not exceed
0.0015.
If replacing, firstly, remove the decorative facia (removal is the reverse of fitting as detailed in sec-
tion 8.4). The catalysts are located on the top of the internal firebox and can be removed by
unscrewing the retaining nuts securing the clamping plate. Remove the catalyst and its seal and dis-
card.
Refit a new catalyst and seals in reverse order, ensure the catalyst and door have good seals.
TESTING FOR FIREBOX LEAKAGE
Appliances that are several years old or have been extensively dismantled should be checked for
soundness. It is important that all the products of combustion pass through the catalytic converters
at the top of the firebox before leaving the appliance.
The firebox is heated by lighting for a few minutes to provide a flow through the firebox. The burner
is then shut off and a smoke pellet or match introduced at the base of the fire underneath the burner
tray. Large quantities of smoke will emerge from the top of the appliance, but none should emerge
from the joints or gasket faces, especially around the door. It is important to note that the appliance
can never be expected to be 100% smoke tight and small quantities of smoke may be seen in cor-
ners of joints and gasket faces etc without affecting safety when the fire is in operation.
CO (%)
CO2 (%) = ratio
9
10.3
10.4
