overheating boiler.

[baggins]

Hi,
Was wondering if anybody could help, i have a Baxi solo 3 pfl boiler and a grundfos ups 18 60 pump. Also a honeywell 3 way valve. I noticed yesterday the rads were not on when i awoke so i looked at the timer and it said heating was on so i checked the boiler which was off with the overheat light on. I reset the boiler and 20-30 mins later it had overheated again. I have also noticed that the water pump seems to be pumping when i have neither HW or CH on, i know they do over run for a few mins but i dont think its that. Today i put on the hot water without the CH to see if the boiler would overheat and when it fired up it was banging really loudley and making all kinds of strange noises. I went up to the header tank to ensure there was water there and there was but it was warm! I have removed the cover from the motorised valve and got the mrs to first switch hw on and then off and then do the same with the ch and the 3 way switch seems to be doing what it should so im thinking from reading through all the great advice and help on this forum that maybe it could be the pcb which i do understand is quite a common problem with this boiler.
It isnt something i would do myself but it would be good to have some kind of knowledge of the problem when i get someone out.
Any help, advice would be greatly appreciated.
Many thanks

 

[gas4you]

Sounds like the pump could be stuck.

No pump = no flow = banging pipes = boiler overheat.

 

[baggins]

Hi gas4you,
thanks for your reply, unfortunately its not the pump. I have removed silver screw on the front and the pump is spinning quite freely.i can also hear it speeding up and down when i increase or decrease the speed. Today i have noticed that with the ch and hw switched off the boiler still sounds as if its still running although it isnt lit.When i switch the boiler off at the mains and then back on it will fire up and run normally until i turn off the hw or ch and then it just shuts off and the overheat light comes on.if i put the hw or ch back on, reset the switch it all comes on fine and will run for hours untill i turn off the ch or hw and as soon as i do that the overheat light comes on and the boiler shuts off. Also when i went to bed last night the ch and hw were both off but the boiler just sounded like it was on, i had to get out of bed and switch it off at the mains.
Thanks anyway

 

[Agile]

You are not meant to turn off the mains supply to the boiler as it needs a live feed to run the pump overun.

Its difficult for me to guess whats wrong based on what you have told me.

You should check the wiring of the system, do a thermal survey and you might then conclude the PCB is faulty.

Tony

 

[baggins]

Thanks for your reply tony, i kinda guessed i should,nt switch the boiler off at the mains but the pump had stopped pumping it was the boiler that was that was still going although not fired up hours after the hw and heating had gone off, no reason for the boiler to be doing anything except going to sleep like me. I have a heating guy coming tomorrow so hopefully he will sort it out.
once again thanks