boiler overheats after serval hours

[ex-man]

Hi,

The problem I seem to have with my boiler is that after a couple for hours (any thing between 2 to 6 hours) the boiler will overheat and shut down. When reset the boiler will work fine – both hot water and central heating appear to be fine while the boiler is working.

The boiler is an Ideal Classic LXFF

 

[ChrisR]

First thing to find out is whether it actually hoverheats or does it just appear to from the overheat stat. You would expect it to make a racket if it's boiling. Otherwise it could of course be a faulty stat - Corgi job.

Check if theres an air bleed point in the airing cupd where the pipes go into the cylinder.

 

[ex-man]

Well,

The hot water is not scalding, and the radiators are not dangerously hot. I have checked for air and bled the system all seems fine there. I was told by someone that the system may need to be pressure cleaned, but on draining the system the water appeared to go from clear to orange and back again.

J.

 

[kevplumb]

could be a dodgy high limit stat or a bad connection ?

 

[ChrisR]

It's looking that way unless.... has that boiler got a thermocouple? It could be getting old

 

[ex-man]

Thanks for the replies gentlemen. Just one other thing to add is that the header/expansion tanks get hot while the system is running and the overflow from the header tanks seem to drip while the system is running.

Would this lead you to believe the boiler is getting too hot?

J

 

[kevplumb]

water level to high in tank or pumping over
hence the orange water

 

[ex-man]

Thanks for the reply, but I’m not sure I understand the linkage between orange water and over pumping. I’ve the check the level in the header tank and this seems fine, and the pump was set to its lowest flow rate.

J

 

[kevplumb]

orange water = rust
pumping over lets oxygen into the system =rust once it finds some nice steel rads to play with

 

[namsag]

boiler stat has gone, these are connected to the board by a two pin plug which sometimes becomes loose,disconnect electric and check all push on connectors to board are pushed fully home.If you are getting rusty water you have a serious pumping over problem with far far too much fresh oxygenated water getting introduced to the system (mind you i have saw some inhibitors that turn the water red). you will eventually have holes in every rad and if its been doing it for a long time rads may burst during power flush. Hot header tank will be a mixture of consatnt pumping over and boiler stat gone

 

[ex-man]

Thanks for that information . So I have drained the system twice (leaving about 12 hours between) and added Fernox. hopfully this will stop the boiler from "overheating".

 

[ChrisR]

It won't stop it pumping over or overheating.
Source of all your trubs may be that the level in the header tank is too high. It has to be very low cold so there's room for expansion without overflow, otherwise you bring in fresh water/O2.
Build up of resulting sludge can bring on pumping-over which makes matters much worse.
It won't come out with just a drain/refill. Try something like Fernox HD Restorer for a week. (Empty header & tip it in then drain a bit more water). That's fairly gentle - go stronger if you 're prepared to deal with leaks (which'll find you eventually anyway)
Drain refill drain after the week. Then cut the pipe where the feed joins the circuit, if you can reach it, just to have a look. If signs of deposits you'd best replace the pipe round there.

 

[namsag]

Doesn`t matter how many times you drain it this will only make matters worse by introducing even more fresh o2 inriched water.Classics have a minimum distance in the book between open vent and water level in tank to stop mixing (think its about 8 inches ). by your reply it doesn`t sound like you are taking information in and need a pro to attend. Also if your stat is f##ked its f##ked and draining it wont fix it.

 

[kevplumb]

go with you there mate

 

[ex-man]

Thanks Gentlemen for all your help. You have given me various options which I’ll need to consider. I think I’ll get the stat looked at first, as I have already drain the system.

J