Thermaflow TH12 - Isolation; Checking the Pressure in the Expansion Vessel; Checking the Inline Strainer; Checking the Hot Water Blending Valve

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WARNING: FOR YOUR OWN SAFETY
SERVICING AND MAINTENANCE SHOULD BE CARRIED OUT BY A PERSON WHO IS
COMPETENT TO DO SO.
3.2 ISOLATION
• Before commencing, refer to section 1. Installation
Checking the pressure in the expansion vessel
The primary expansion vessel (volume 25 or 35 litres) is the red or blue vessel connected to the central
heating return pipe near to the boiler. Its purpose is to take up expansion in the boiler and central
heating system.
The pressure can be accurately checked with the pressure relieved on the other side of the diaphragm.
To do this drain some water from the central heating system until the pressure gauge registers zero.
Connect a pressure gauge to the car tyre type valve on the vessel. The pressure should register 150
KPA (1.5 Bar). Refill heating system as described in section 2.7.2
The secondary expansion vessel (volume 2 litres) is the white or silver vessel connected to the cold
inlet of the plate heat exchanger.
Its function is to take up expansion in the hot water pipe work and so protect the blender from damage.
The pressure can be accurately checked with the pressure relieved on the other side of the diaphragm.
To do this, isolate the water supply to the Thermaflow and open a hot tap. Water will run for a few
seconds then stop.
Connect a pressure gauge to the car tyre type valve on the vessel. The pressure should register 350
KPA (3.5 Bar). Close the hot taps and turn the water supply back on.
Checking the inline strainer
Whilst the water is off, remove and clean the gauze in the brass strainer assembly. To remove the
gauze for cleaning un-screw the brass plug.
Checking the hot water blending valve
With the store temperature fully recovered, run a hot tap and check the flow rate and temperature.
If the hot water has deteriorated suddenly (over less than a month) then this points to a problem with
the blender.
A broken blender is usually linked to a loss of pressure in the secondary expansion vessel. The
expansion vessel protects the blender from damage when the water in the secondary system expands
as the water re-heats after water is drawn off.
Check the pressure in the secondary expansion vessel as detailed previously in section 2. If it does not
hold pressure it will need to be changed along with the blender.
Strip off the blender and check hot and cold mesh filters for blockage. (Clean if necessary).