My alpha cb24x combi boiler keeps blowing the main fuse,even when its not on,this can happen in 2mins or 2 days after i redo the fuse using 15 amp wire, why is this happening ?

Some combi boilers have a 'Keep Warm' function. Check to see if your combi has this feature. This is a function where the system preheats an amount of hot water to provide instant hot water when you turn on the tap/faucet. To do this the combi will start up when it detects the stored water is below a certain temperature to reheat it ready for use. This can be turned off if you prefer not to use it.

Thermostat on boiler . or hot water sensor .

could be air presure switch which tells pcb that fan is working and would then bring inn ignition system then main gas valve.Would suggest getting gas engineer in.pommie engineer

If you turn the power off and it's still there then it's not anything electrical in the flat.. it could be transferred noise from another source. I would try locating the sound by listening through a tube to locate the sound more accurately. This method of sound source location is used by old fashioned mechanics listening for engine noises and is very good at finding them..
good luck !

All the combis I've come across merely fail to fire if the pressure is not up. not only do they not fire, nothing else works including the pump and in any event the pump should not overheat just on low pressure.
water loss - try turning off the valves on the flow & return pipes [3/4 inch ones] 1 valve per pipe . This will isolate the rest of the system - rads etc Note pressure over a time period. In this mode the hot water circuit will still work but do NOT use the heating circuit
1/2 bar over 2 days is not serious but it should be found
Once you have either mended the leak in the rest of the system or found there is not one, insist on a replacement boiler
In any event having looked at the reasons given for the fuse blowing, I would definitely get a replacement.
These problems should not happen on a new boiler
I list Worcester.-Ariston-GlowWorm-Ideal- and many others who would confirm this

Assuming this is a combi boiler and you mean that the main gas burner comes on then off:-
How long after - 5-20 secs check overheat thermostat Check the wires to it are firmly in place i.e. making a connection. If Ok? then you can short this out by joining the wires together - do with boiler OFF at mains electricity
Longer - say 1-2 mins check secondary heat exchanger for blockage - usually furred up inside & only solution is replacement

what kind of heater combi? if combi you may be pressurising boiler to high ie over 1 bar boiler may be blowing off through release valve check discharge pipe

reduce cold water pressure

there is a zoneing valve thats suppose to be in the line to keep this from happening, might even have a check valve either way which ever one you have is bad and should be changed with a new one

The first thing you need to do is to put some more water into your heating system. This is usually done by allowing water from your (pressurised) domestic cold water supply to flow into the system: On older boilers, this is done with a connection (often made with a removable hose) on the pipework just outside the boiler. Newer boilers may have a built-in connection with some sort of removable link (sometimes looks like a plastic key).

Once you've got the boiler up to working pressure (typically about 1 bar - 15 psi), you should be able to bleed your upstairs radiator properly.

This may be all it takes, though the pressure excursions you're getting when you run the hot tap suggest there may be another problem. See what happens to the pressure as the boiler heats up and cools down. There really ought to be very little pressure difference between the two conditions. If you see significant changes, this usually means that the "pressure vessel" (or in hydraulic terms, system accumulaor) has lost its air charge.

The pressure vessel is a metal container inside the boiler, usually painted in red enamel. Somewhere near the top, you will find a schrader valve (like the one on a car tyre), and you can use this along with a tyre pump to replenish the air in the top of the vessel. This will reduce your pressure transients for a while, but you need to keep an eye on it. If the problem returns, you probably need to replace the pressure vessel (or clag another one into the plumbing alongside the boiler).

A.