help with worcester combi

[nabby68]

My girlfriend has a worcester combi 24 i boiler fitted. It is approx 8 years old and she has had problems with it for many years. I decided to contact Worcester who gave me a fix price to try and sort it out. The engineer replaced several parts in it. The boiler was working after the engineer had been but 1 month later the hot water would not work, so, re-contacted Worcester who sent out a further engineer who said it was a different fault and therefore another £210 . It was fixed and working. Then again the boiler decided not to work properly and i am very reluctant to call Worcester out as ive already spent over £400! I do have some knowledge on central heating systems and though i would try this forum for help.
The problem with the boiler at the moment is that the pressure goes up sharply when it is switched on but this takes several attepmts to get it going as it goes into lockout a few times before it lights. Then it blows off through the pressure relief valve and then the boiler cuts out. Also it is very very slow to refill it up to the required pressure but that may be due to me not having the filling key inserted correctly and i have looked at the faq's for this. My girlfriend also mentioned that she though that the system was never cleaned when the boiler was first installed, so im thinking that maybe it is full of crap which may not help the situation.
Could someone give me a process to follow to help
Thanks

 

[buck51]

Check the expansion vessel, you can find the info you need in FAQ section

 

[nabby68]

thanks buck 51. would that be the first thing i should check? and would the possible sludge be a problem?

 

[BingoBongo]

if its locking out and blowing off before it even lights i would be looking at pos pump/blockage

 

[nabby68]

if its locking out and blowing off before it even lights i would be looking at pos pump/blockage

its locking out before it blows off and it takes several goes to re-light it then once its lit the pressure rises until it blows off.
i hope this explains it a little clearer

 

[nabby68]

any help fellas?

 

[lkuya]

just get a new boiler mate

 

[nabby68]

UPDATE:
i re-pressurised the expansion vessel and then re-pressurised the whole system to 1.5 bars. Then bled the rads and started the boiler up. After several intances of the burners firing up then cutting out and with the pump making a very strange but not loud high pitched screeching noise i sbled the pump but hardly no air came out. Ithen tried to fire up the boiler again a couple of more times and the noise from the pump became less and less until it stopped and the boiler stayed lit!
My girlfriend also informed that the rad in the bathroom had stopped working over 12 months ago!
I am now convinced the system is full of sludge and blockages and the systrem is piped in 10mm pipe so quite easy for it to be blocked i guess.
So i think a sludge remover may be the next move.
Does anybody else have any thoughts on the matter
thanks

 

[gigz]

First of all drain all the water out, take off the rads and flush with a hosepipe (best to bash the sides with a rubber mallet to loosen any crud) Take one of the rad tails out and attach it to the hosepipe, now connect this to each valve in turn and pressurize the boiler and let flow until water is clear (get someone to do this as they can watch the dial for you) Put rads back on and add some X800 and run the system as often as possible for at least 4 hrs then drain, refill with clean water and run for 1/2 hr, drain again add some X100, job done (better to fit a magneclean or spirovent when its drained down). Lot of work i know but worth it in the long run. Then again the pump might be pooped

 

[tonybhoy]

Auto air vent in the boiler could be the culprit.

Tony.

 

[gaspro1981]

Auto air vent in the boiler could be the culprit.

good shout me thinks

 

[nabby68]

can you elaborate on the auto air vent theory a bit more please?

 

[bengasman]

The i-series is a cowboy favourite, and most likely not installed properly.
Your guess it was not cleaned is probably correct too.
Corrosion will kill the pump and aav.
aav will either leak, or stick shut in which case the air stays in the boiler.
Pump on its last legs can also be what you hear.
Clean system first,
replace aav
new pump if in doubt.

 

[nabby68]

thanks bengasman.
But i havnt noticed any leaks from the aav. And the fault now is that sometimes the boiler will fire up correctly and sometimes it doesnt but once it does it stays lit. Would this be caused by a faulty aav?
Also the DHW is fine when called for and the boiler fires up no problem. So, maybe a dodgy pump? How would i check for this and would that cause the fault i am having?

 

[bengasman]

Start with cleaning the system and see what happens