iv)
Unscrew the bolts (Fig 6.7.3 item 94) securing the gas inlet pipe to the gas
control valve.
v)
Remove the four nuts securing the combustion blower (fig. 6.7.3 item 100)
outlet flange to the burner and remove the combustion blower.
vi)
Reassemble (Section 8.3)
NB:
When reassembling inspect any gaskets for damage and replace if
necessary.
8.4.8
Gas Control Valve /Venturi Assembly
(Fig. 6.7.3 item 163)
i)
Isolate the appliance (Section 8.1)
ii)
Gain access (Section 8.2)
iii)
Remove the push on connector block to the gas valve.
iv)
Unscrew the bolts (Fig 6.7.3 item 94) securing the gas inlet pipe to the gas
control valve.
v)
Unscrew the bolts securing the gas valve (Fig 6.7.3 item 106) to the inlet port
of the combustion blower.
vi)
Remove the gas valve/venturi assembly as a complete unit.
vii)
Unscrewing the union fitting from the gas valve.
viii)
Reassemble (Section 8.3)
ix)
Check the gas rate and combustion (See Section 5 - Commissioning)
NB:
Always change the gas valve/venturi assembly together. This
assembly is factory preset but must be checked using the procedure
set out in Section 5.7 (Combustion testing).
8.4.9
Flow Overheat Thermostat
(Fig. 6.7.2 item 47)
i)
Isolate the appliance (Section 8.1)
ii)
Gain access (Section 8.2)
iii)
Remove the push on connector from the sensor taking note of the correct
position.
iv)
Unscrew the bolts securing the stat (Fig 6.7.2 item 60)
v)
Reassemble (Section 8.3)
NB:
When fitting the new thermostat it is an advantage to smear a thin
film of
heat sink compound between the thermistor and pipe. This,
combined with fitting the new thermistor tightly to the pipe, ensures a
good contact.
8.5
SPARK IGNITION/FLAME DETECTION ELECTRODE
(Fig. 6.7.2 item 43)
i)
Isolate the appliance (Section 8.1)
ii)
Gain access (Section 8.2)
iii)
Remove the pull off HT lead to the spark ignition electrode.
iv)
Undo the screws to the spark ignition electrode flange
located on the heat exchanger
top panel (Fig 6.7.2 item 56) and withdraw the spark ignition electrode.
v)
Reassemble (Section 8.3)
NB:
When reassembling inspect the gasket for damage and replace if necessary.
With the new spark ignition electrode in place it is essential to ensure the gap
between the tip of the electrode and the burner surface is 4 mm. Distances
above or below 4 mm will affect ignition performance. If necessary gently
bend the electrode taking care not to damage the ceramic insulator.
8.6
BURNER
(Fig. 6.7.2 items 42)
i)
Isolate the appliance (Section 8.1)
ii)
Gain access (Section 8.2)
iii)
Remove the combustion blower (Section 8.4.7)
iv)
Remove the 4 nuts fixing the burner to the top of the heat exchanger (Fig 6.7.3, item
100).
v)
Remove the spark ignition/flame detection electrode (Section 8.5)
vi)
Withdraw the burner from the top of the heat exchanger.
vii)
Reassemble (Section 8.3)
NB:
When reassembling inspect any gaskets for damage and replace if
necessary.
WD440/3/2007 Chapter 8 : Replacement Of Parts
The Keston Qudos 28h & Qudos 28hP
Boilers
Installation & Servicing Instructions
Page : 47
