Potterton Derwent Compact Plus Installation, Operation & Maintenance Manual page 12

SECTION 4
PAGE 10
Control & Safety Equipment
1. Low Gas Pressure Switch
2. Control Box Dungs
3. Air Pressure Switches
4. Overheat Thermostat
5. Secondary Heat Exchanger Overheat Thermostat
6. Combustion Chamber Overheat Thermostat
Set-up components
1. Damper for air flow control at 100% load
2. Rheostat for air flow control at 80% load
3. Control Board
Working Principles of the Derwent Compact Plus
Condensing
The boiler has been designed to work as a two stage
High/Low boiler. Full load (100%) for second stage
and low fire (80%) for first stage. The firing of the
POTTERTON COMMERCIAL PRODUCTS DIVISION
INSTALLATION, OPERATION AND MAINTENANCE MANUAL
DERWENT COMPACT PLUS - CONDENSING
boiler works to the following operation:
1. Pre-purge takes place for a duration of 40
seconds during which the pressure switches are
tested. If the pressure switch for the second stage
is not satisfied, but the first stage is satisfied, the
cycle will go to the next step.
2. Pilot lights during the next 10 second period.
3. Main burner establishes and cross lighting takes
place. The boiler will remain for 60 seconds on
first stage operation, even if the second stage
thermostat is calling for heat. The main valve
contains a regulator which is in charge of first
stage operation.
4. The boiler moves from the first stage operation to
the second stage operation (Nominal load) and
remaining on this setting until the thermostat is
satisfied. The main valve with its regulator ensure
the second stage operates correctly.
HYDRAULIC TEST OF BOILER
This is to be carried out on boilers assembled on site
or where water manifolds have been disturbed.
Fit a hydraulic test pump to the return manifold and fit
a valve to vent air from the flow connection.
Fill the boiler with cold water and, in accordance with
BS 779: 1976, pressurise up to 1.5 times the design
pressure, ie. 4.5 bar maximum, and observe for 30
minutes.
Connecting the Water System
The flow and return connections should be made to
the
recommendations of CP342 and PM5.
It is essential that all pipework connections to the
boiler are self-supporting, correctly aligned and allow
for free expansion of both boiler and pipework.
Care should be taken in the pipework design to
prevent strain on the connections. Excessive strain
can leak to premature failure of the boiler, which is
obviously outside the terms of our warranty.
The use of expansion bellows to take up both axial
and lateral movement is recommended.
The flow and return connections are made at the rear
of the boiler.
Condensate
The condensate siphon of the secondary heat
exchanger is at the rear of the boiler. It is only
permissible to drain the condensate directly into a
domestic sewer system when the system consists of
corrosion-resistant materials (e.g. PP pipe, stoneware
appropriate manifolds following the