Horne Engineering Ltd
Issue 3 8/05 9
FAULT FINDING CHART
SYMPTOM
POSSIBLE CAUSE
ACTION
Mixed water temperature too
high
Temperature setting too high.
Temperature has been set when the hot water
temperature is too low
Re-adjust temperature setting
Hot water has migrated into cold water supply
Inspect Check Valve at cold inlet
If the check valve leaks replace the strainer
body and check valve sub-assembly
Thermostat Element has failed this can be checked
by carrying out a hot or cold water failure test.
Replace element (8)
Mixed water temperature too
low
Temperature Setting too low
Re-adjust temperature setting
Hot water supply temperature has fallen
Check hot water supply system
Cold water has migrated into hot supply
Inspect Check Valve at hot inlet
If the check valve leaks replace the strainer
body and check valve sub-assembly.
Cold valve face requires cleaning
Remove valve Cover (5) and service valve face
Mixed water flow rate too
low.
Partly blocked strainers
Clean strainers
Unusually high pressure drop in supply pipework
Check all valves are full open.
Check Pressurisation unit
Check mains supply
Extra Demand added to system
Check pipe sizing
Mixed water temp does not
respond to adjusting screw
Slide-Valve (9) is seized
Valve requires de-scaling
Hot and cold inlets reversed
Remove HORNE 15 TMV from pipes and
reverse connections.
Connect inlet with red dot to hot pipe
Mixed water temp changes
and is not steady
Slide-Valve (9) is seized
Valve required De-Scaling
Thermostat element has failed (This can be checked
by carrying out a hot or cold water failure test)
Replace elements (8)
Water at outlet runs full hot or
full cold
Hot and cold inlets are reversed
Hot inlet is marked with Red dot
Cold inlet is marked with Blue dot
Valve continues to pass cold
water when hot supply is
isolated
Cold valve face requires cleaning
Remove valve cover (5) and service cold valve
face
Valve continues to
pass hot water when
cold supply is isolated
Fouling at hot valve seat
Clean hot valve face
Slide-Valve seal is damaged
Replace Slide-Valve Seal (13)
Element has failed
Replace Element (8)
