Keston Qudos 28s User, Installation And Servicing Instructions page 66

Qudos 28s and Qudos 28h
Gas valve/Venturi assembly replacement procedure for
KESTON Q28s, Q28sP, Q28h and Q28hP boilers.
These conversion instructions must be read in conjunction with the Keston Qudos 28s/28sP or Qudos
28h/Q28hP Installation & Servicing Instructions - WD420 and WD440.
Before proceeding to the replacement procedure please check if the tamper paint on the offset adjustment cap
(see attached picture) is intact. If the tamper paint is broken please return the assembly to KESTON
BOILERS.
Do not dismantle the gas valve/venturi assembly. Always change the gas valve/venturi assembly together.
To replace the gas valve/venturi assembly you must carry out the following sequence:
1. Isolate the appliance (Section 8.1)
2. Gain access (Section 8.2)
3. Remove the push on connector block to the gas valve.
4. Unscrew the bolts (Fig 6.7.3 item 114) securing the gas inlet pipe to the gas control valve.
5. Unscrew the bolts securing the venturi (Fig 6.7.3 item 122) to the inlet port of the combustion blower.
6. Remove the gas valve/venturi assembly.
7. Unscrewing the union fitting from the gas valve.
8. Reassemble (Section 8.3)
9. Check the gas rate and combustion – MANDATORY
Although the gas pressure is preset at the factory it is required to assure proper combustion by measuring
gas input and the level of carbon dioxide, or oxygen and carbon monoxide, in the flue outlet from the boiler.
Over firing or under firing the burner will reduce the longevity of the appliance and may result in excessive
carbon monoxide levels
Carbon dioxide and carbon monoxide are colorless, odorless gases produced by all combustion
processes. When the Keston condensing boiler is operating properly, carbon dioxide (CO2) levels will be
between 8.4 & 8.8% (low rate) and 8.9 & 9.3% (high rate) and carbon monoxide (CO) levels will be between 5
& 20 ppm (low rate) and 50 &150 ppm (high rate) for natural gas. For LP gas, carbon dioxide (CO2) levels will
be between 9.5 to 9.9% (low rate) and 10.3 to 10.7% (high rate) and the carbon monoxide will be between 5
to 20 ppm (low rate) and 50 to150 ppm.
In any event, the CO2 level at low rate must ALWAYS be less than CO2 levels at high rate.
To measure CO2 levels in the Keston boiler remove the 1/8" plug from the flue outlet pipe spigot (Figure
6.7.4 item 17). Insert the probe of a calibrated combustion analysis meter and sample the gases as instructed
in the test equipment's instructions.
When firing the boiler for the first time since installation, the CO level at high rate may be between 100 &
220 ppm and between 50 & 80 ppm at low rate. This is due to compounds used during manufacture curing
within the combustion chamber. On boilers which have been fired for more than one hour since installation,
the CO levels should not exceed 150 ppm at high rate and 50 ppm at low rate. If CO levels above these
values are experienced, the combustion chamber and flue system should be investigated.
The Qudos 28s is factory set for combustion and should need no adjustment. However, in the event
adjustment is required.
Check combustion errors are not a result of incorrectly installed flue and/or air system, terminal location or
damage or debris on the burner. If all these factors are found to be in order precede as follows:
1) Set any controls to call for heat.
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WD478/0/2008