Knock from the combi.. All aspects of plumbing questions and answers, help, tips and information

[smashngrab]

When the heating is on and somebody turns a hot tap on,we get a knock from the combi (Valiant) only when the heating is on though.Its just one knock,getting on my nerves a bit,any ideas.
rob.

[ALDA]

ROB,

SEEMS LIKELY THAT THE DIVERTER VALVE IS PRODUCING THE "KNOCK"
NOISE.

THE VALVE WHEN NEW WILL OPERATE SMOOTHLY BUT WITH AGE AND VALVE BECOMING STICKY DUE TO CONTAMINANTS (LIME SCALE OR SLUDGE) THE RESULT CAN BE WHAT YOU ARE EXPERIENCING.

ALDA.

[smashngrab]

[quote="ALDA"]ROB,

SEEMS LIKELY THAT THE DIVERTER VALVE IS PRODUCING THE "KNOCK"
NOISE.

THE VALVE WHEN NEW WILL OPERATE SMOOTHLY BUT WITH AGE AND VALVE BECOMING STICKY DUE TO CONTAMINANTS (LIME SCALE OR SLUDGE) THE RESULT CAN BE WHAT YOU ARE EXPERIENCING.

ALDA.[/quote]

Thing is,that diverter valve was changed after just over a year.We noticed a rad in the kitchen was getting luke warm,without the heatng being on.Changing the valve sorted it out,cant be nothing else?.

Unless the bloke used a second hand one!
rob.

[ALDA]

IF THE VALVE WAS DODGEY AFTER A YEAR AND IT NEEDED TO BE REPLACED, THEN HOW LONG HAS THE NEW VALVE BEEN IN?

WAS THE SYSTEM FLUSHED AND DRAINED AND INHIBITOR INSTALLED AT THE TIME OF THE VALVE REPLACEMENT?

HAS THE KNOCK JUST APPEARED OR HAS IT GOT GRADUALLY WORSE?

IS THE C.W. SUPPLY PIPE SECURELY CLIPPED?

IS THE C.W. SUPPLY PRESSURE EXCESSIVE ? (TRY TURNING THE STOP COCK OFF SLIGTHLY).

[htg engineer]

I agree with ALDA, check the cold and hot water pipe are clipped etc.

If it make the noise everytime, try holding the pipes whilst someone turns on the hot tap. If the noise is still there, from inside the boiler is could be the diverter.

Also - could be the gas valve but it would make the noise with both heating and water, unless you just haven't noticed when the heating has been on.

Htg

[smashngrab]

I cant remember the system being drained.can it be done without draining,would it muck it up?there was no inhibitor put in i know that.there is now though.I'll turn the water down a touch,and see what happens.i'll check those pipes also.
rob.