Boiler problem, worcester 26CDI XTRA, help please

[zaskar]

I have had a problem with my boiler for over a year now, just been putting up with it really. As far as i know it seems to work ok but for this problem, pressure ok, i am an electrician so i am willing to fix it myself, just need to know what might be wrong please.
When having a shower (combi boiler- i have no cylinder) the water will come through hot after about 3 minutes, and will only last hot around 5 minutes, then will go ice cold for about 3 minutes then will come back on hot for about 5 minutes........
this goes on and it is really a pain in the arse!! it just keeps going hot cold hot cold hot cold, and so on.
Could it be a stat or valve or something?
please help.
thanks

 

[nickso]

could be scale, thermistor,diverter valve. would need far more info to make a proper diagnosis.

these are not the easiest of boilers to work on. some professionals will not even go near them so you might be on a hiding to nothing trying to fix it yourself. you may be better off caling worcester for a fixed fee repair with a warranty on it.

edit. the most important question i forgot to ask was does it do the same on all of your taps as well? if not it is probably the shower stat that is faulty.

 

[zaskar]

could be scale, thermistor,diverter valve. would need far more info to make a proper diagnosis.

these are not the easiest of boilers to work on. some professionals will not even go near them so you might be on a hiding to nothing trying to fix it yourself. you may be better off caling worcester for a fixed fee repair with a warranty on it.

Thanks for the reply, its out of warranty, i do live in a very hard water area...
please ask for any info to try to narrow it down?

 

[nickso]

well a few things to check.....

heating off, pipes as cool as possible.

switch on tap, does the boiler fire up within a few seconds? check the diverter from underneath (middle of boiler.big brass thing), right hand side of DV is a big brass disc. attached to it is a black plastic microswitch, if you look closely you can see a rod with a black plastic plunger that should hit the microswitch when the tap is turned on, it should stay there for the duration of the water demand. does it?

while the boiler is supposedly firing for hot water do the larger 22mm pipes underneath the boiler get hot? best to feel about a foot away from bottom of boiler to avoid being confused by heat transfer of the pipe.

after this you will need to get the multimeter you undoubtably have ready for some action.

 

[nickso]

oh yeh and you still havent answered the first question ......do all of the taps do the same as the shower?????

 

[zaskar]

oh yeh and you still havent answered the first question ......do all of the taps do the same as the shower?????

The shower is a thermo mixer, but i have checked the two pipes that feed it and the hot pipe does go cold, so i illiminated the mixer being the problem, but i have not checked the kitchen hot tap, which is not a mixer, thanks for the reply, a multimeter is sat right next to me here by the pc.

 

[zaskar]

Although i havent checked the ch side of the boiler to see if that goes cold as well, the heating overall in the house seems to be ok, it is all underfloor plumbed heating, no rads at all.

 

[zaskar]

And another thing, sometimes the boiler itself seems to click constantly, quite noisy, over and over.

 

[bengasman]

run your basin tap or any other tap that is not a mixer and see what happens. you need to isolate the problem, fault finding on boilers is same principal as on electrics