Keston C40 Installation And Servicing Instructions page 60

C55, C40, C C55, C40, C C55, C40, C55P C55, C40, C
Gas valve/Venturi assembly replacement procedure for
KESTON C55, C40, C55P and C40P boilers.
These conversion instructions must be read in conjunction with the Keston C55 & C40 Installation &
Servicing Instructions – WD265.
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 7.1)
2. Gain access (Section 7.2)
3. Remove the push on connector block to the gas valve.
4. Unscrew the bolts (Fig 6.7.3 item 149) securing the gas inlet pipe to the gas control valve / venturi
assembly.
5. Unscrew the bolts securing the gas control valve / venturi assembly (Fig 6.7.3 item 81) to the inlet
port of the combustion blower.
6. Remove the gas valve/venturi assembly as a complete unit.
7. Reassemble (Section 7.3)
8. 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 colourless, odourless gases
produced by all combustion processes.
When the Keston condensing boiler is
operating properly, carbon dioxide
(CO2) levels will be between 8 & 8.2%
(C40 low rate), 8.3 & 8.5% (C55 low
rate), 8.2 & 8.7% (C40 high rate) and
8.6 & 9% C55 (high rate) and carbon
oxide (CO) levels will be between 5 to
20 ppm (low rate) and 50 to 150 ppm
(high rate) for natural gas. For LP gas,
carbon dioxide (CO2) levels will be
between 9.3 & 9.5% (C40P low rate),
9.6 & 9.8% (C55P low rate), 9.8 &
10.3% (C40P high rate) and 10 &
55P & C 55P 55P & C40P & C & C
1/2
WD483/0/2008
40P 40P 40P