Keston Thermomatic RSM20/FB, Installation & Servicing Instructions Manual, Page: 5 / 46

Page 5
1 GENERAL DESCRIPTION (Fig.1.1)
The Thermomatic RSM 20/FB is a wall mounted
water jacketed vertical tube Combination Boiler fitted
with a copper coil to give an immediate supply of hot
water.
The appliance is room sealed and fitted with a coaxial
duct for fan powered ventilation, designed for exit to
either side or to the rear of the appliance.
The copper coil containing 2 litres of hot water is
indirectly heated, giving an immediate and continuous
hot water supply.
The central heating pump will not operate until
the boiler temperature reaches 60°C
. The pump is
controlled by a capillary thermostat called the anti-
condensing thermostat. In addition, a bimetallic
priority thermostat will stop the pump as soon as
domestic hot water is drawn. This allows the full heat
output to be directed to supplying hot water only.
The appliance jacket extends to burner level, so the
walls of the combustion chamber are water-cooled.
This prevents the intense local heating usually
associated with combination boilers and considerably
prolongs the appliance life.
The domestic hot water, being indirectly healed
through a coil of a larger diameter than normally
used, is not so easily affected by calcium impurities
that build up lime scale. This together with the flexing
of the coil due to temperature changes, means
calcium "build-up" is considerably lessened.
With the Summer/Winter switch set to Winter the
appliance will automatically adjust to the central
heating output, which may be a single radiator, ot
any number within the heat ouput of the appliance.
The Thermomalic does not require a 'by-pass' and all
radiators can be fitted with thermostatic radiator
valves.
Unlike many other combination boilers, the Ther-
momalic will operate on low water pressures. The
boiler within the casing is cylinder shaped and fitted
with vertical copper flue tubes through which the gas
products pass. These tubes are fitted wiih stainless
steel baffles to increase efficiency and to rapidly
conduct the heat from the gas products to the water
contained within the cylindrical heat exchanger.
An extended copper coil fitted around the vertical
flue tubes is within the water content. The water
content connects to the central healing system and
indirectly heats the domestic water passing through
the coil.
A SIT Controls multifunctional control with electric
ignition is used and temperatures of both central
heating and hot water ate controlled by capillary
thermostats.
The flue extract fan incorporates a pressure control
switch which activates the gas control. In the case of
a fan failure of any kind the gas control fails to safely.
It is recommended that a scale inhibitor should
be fitted in hard water areas.
FIG.1.1 INTERNAL DESIGN
1 Manual air vent cock
2 Gas control valve
3 Stainless steel burners
4 Ignition electrode
5 Pocket for an anticondensing thermostat phial
6 Pocket For safety thermostat phial
7 Pocket for boiler healing thermostat phial
8 Water temperature gauge
9 Automatic air vent
10 Fan motor
11 Expansion vessel
12 Stainless steel Hue baffles
13 Boiler shell
14 Domestic hoi water copper coil
15 Circulating pump
16 Pressure relic! Safely valve
17 Water pressure gauge
18 Bimetallic priority thermostat
19 Air pressure microswitch
20 Air pressure switch body
21 Concentric flue/air pipe
22 Flue terminal
23 Flue hood
24 Electronic control box
25 Room sealed combustion chamber
26 Flame detection probe
27 Mini expansion vessel (Domestic)