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knocking in systems is from fluid hammer in the pipes
It can be controlled in the first instance by the proper mounting of the pipes in the saddles ( more saddles the better --- less chance for the pipe to hit the wall or brackets )
The "hammer" occurs when a valve is opened and fluid stats to flow then the valve is shut off rapidly . the fluid is still flowing and so it hits that valve and the pressure builds up in the pipe ( knock) the valve is again opened reducing the pressure in the pipe only to shut off quickly again making the pressure again build up ( knock)
The are devices called accumulators available fro good plumber suppliers shops , that have a gas filled bladder in the unit
When the valve shuts off quickly , the flow of the fluid is absorbed against the gas filled bladder and then released when then valve is again turned on
this smooths out the stop/start action of the fluid and so stops the hammer or knock
The noise should be treated seriously as it will loosen of fittings and joints causing leaks and if extreme , will split pipes
As an example of what I am talking about take your garden hose and fit a stop hand piece to the end of the hose . turn the tap on , you will see the hose move as the water pressure builds up in the hose
press the trigger and see the hose relax
stop the flow quickly and again see the hose react
That relaxing and reaction of the hose is water hammer or knocking but you won't hear it in a hose , but with rigid pipes the action comes out as a vibration , like a drum being hit
I am not a expert by any means but have a similar problem with an outside boiler, but mine is in a garage. It strikes me that if yours is located in a more confined space you could place a small parafin heater in the cupboard which would raise the temperature sufficiently to stop the frostat activating the boiler and also be sufficient to protect the pipes from frost. Hope this helps. John.
TURN WATER OFF TO UNIT AND ALL POWER AND GAS. EXTRACT ALL WATER AND REPAIR PLUMBING TO THE BOILER. IF WATER IS COMING OUT FROM THE BOTTOM, REPLACE BOILER... IF PLUMBING WAS REPAIRED SUFFICIENTLY AND NO WATER IS PRESENT...TURN ON WATER AND CHECK FOR LEAKS THEN TURN ON ALL POWER AND GAS TO THE UNIT AND RELIGHT PILOT....BE SURE THERE IS NO SMELL OF GAS PRESENT WHEN YOU LTE THE PILOT..IF IT DOESN'T LITE YOU MAY HAVE TO REPLACE THERMOCOUPLE OR CLEAN BURNER.
near one corner of the gas valve is a slottedplug.
It looks like large screw headremove the plug just like any screw. This lets you access the gas pressure adjustment screw.
Usually no more than one half to one full turn is needed. (clockwise to increase pressure)
It is important that you not have to much Gas pressure as this will cause overheating and premature heat exchanger failure.
The best thing to do is check the pressure going into the gas valve, and also coming out. Make sure the inlet side of the GV is not partially clogged where the pipe comes in. (especially if you have copper pipe with natural gas)
it sounds like the system was not cleaned properly when the new boiler was fitted. all new boilers need to have the pipework flushed to remove any debris scale sludge and flux from the system. this is now usually done by a power flush which is basically a big pump mounted on a big bucket and it washes the dirt out of the pipework and collects in the bucket. if this is not done the dirt will block up the small passages in the heat exchanger. i suggest the system is cleaned flush and the heat exchanger changed to help protect the boiler a filter should be fitted (for example a magna clean) if the company who installed the boiler is corgi registered then they are liable for the damages. call corgi for advice.
Firstly your system needs a power flush to get rid of the grot, then it needs a good inhibitor to slow up the reappearance of the sludge.
Changing the boiler won't help. Any boiler will get clogged up but the halstead DHW heat exchanger is particualrly prone to getting gummed up. You can clean this out and refit without having to buy a new one. - but without a power flush it will happen again.
You could try resetting this as it could be caused by several factors (blown heat exchanger being one as Karl mentioned). Hve you tried resetting from in Service Mode ?
To get to Servce mode you need to go ino User Setup Mode first (turn off the boiler via the panel switch - then hold the Lock/Reset button whilst turning back on). Once in User Setup Mode if you rotate the thermostats all the way clockwise (it should display the software version) Then press and hold the Lock/Reset button for 3 seconds. This should put you into service mode and it is now possible to change/reset some of the control parameters. If you try resetting the error.
This issue may be caused if the Flue or water stat is tripped (in which case reset the stat). If th Fan resistor remains open in the circuit then you will need tsomeone out to investigate as that may cause the GAS error too.
COuldalso be the Valve coils are faulty in wich case they need replacing (agians I would get an engineer outto confirm and do that).
I'm suyou probably tried all this but just in case...
If the roblem is solved can you advise what fixed it ?