Biasi 24S (2000) cuts out on CH after 2 hours...??

[BENRIBBANS]

Our boiler has had this fault for a few months. It will run happily for a few hours then cuts out. This generally only happens on CH as we never run the hot water for more than 20 mins or so.

BG say I need a new boiler as it would cost about 1k for them to fix by replacing both heat exchangers and a flush so I would be better off bnuying a new boiler. The boiler is only 8 years old, and although not that great, does suffice for our small 2 bed cottage.

I have turned down the temp on the CH but still the rads are very hot, even though they are fitted with TRV's on about 2-3. Obvioulsy the boiler is overheationg and I assume due to limescale/sludge in the main heat exchanger? Would it be worth me trying a manual flush using some X400/X100? We did have the secondary exchanger flushed by BG over a year ago for a similar fault which worked up until now, so maybe doing the same would give us another 12mnths or so? Would it be possible to remove the main heat exchanger to flush properly or is this a corgi-only job?

Any advice greatly appreciated. Thanks.
Ben

 

[gas4you]

I note you say that the ch boiler stat appears to make no difference to the rad temp where ever it is set.

Has the ch thermistor/ntc been checked/replaced. This would be my first port of call. The boiler could just be working on the overheat stat

Failing that if it is only doing it on CH then I would not bother too much about flushing the plate HE.

You don't need to remove the main HE to flush it. It can be done insitu but with the external heating circuit isolated from the boiler.

Personally I would use X800 and let it run through the system for the 2 hours or so that the boiler works, then drain and flush each rad with cold mains via the filling loop.

As I always say, powerflushing can be very good, but it is highly over rated and the same results can be acheived without an expensive power flush.

 

[mehran]

gas4you is spot on about checking the ntc. when the flow ntc goes open circuit the boiler thinks it is always cold and fires at full rate till it over heats. bg is are just playing silly buggers as usual.

x800 is good stuff but bloody strong, if x800 is use make sure that it is flushed out well and x100 is added afterwards.

 

[Agile]

You say the boiler "cuts out" but dont clarify how.

There are two possibilities. The o/h stat which is reset by pushing the tiny button under the black screw on cover.

If thats what its doing then its almost certainly overheating and if the gas settings are correct then that will be as a result of the CH sensor going open circuit. The resistance can be checked.

The other possibility is an ignition failure causing the red light to come on. The cause of that will be something other than overheating and most possibilities would need a CORGI.

With the CH knob at minimum the rads should be warm but not hot and easily keep you hand on the tops. If its hotter then that implies the sensor has failed.

Tony

 

[BENRIBBANS]

Thanks for the replies - I wasnt expecting any replies so quickly!

To clarify, it is the small red button under the black knob. If I leave the boiler to cool for 10 mins or so and push the red button back in, it works again for another few hours or so. The heating is on now so I will check the rads as Tony suggestes although the boiler is definately not on all the time during the 2 hours the CH works for, it does switch off and re-ignite. The outer cover of the boiler does seem to get hot to the touch - like the temp of a rad before it cuts out though.

So if I do need to flush just the boiler, how do I do it? I know how to drain it and isolate it from the CH circuit but how do I still operate the boiler with the valves shut and how do I get the X800 in the system? via the filling loop and an adaptor?

Thanks again,

Ben

 

[gas4you]

Has the ch thermistor/ntc been checked/replaced. This would be my first port of call. The boiler could just be working on the overheat stat

Am I made of glass

 

[Agile]

You are making wrong assumptions about sludge/scale in the boiler.

There is nothing identified yet which indicates a need for that.

Please turn CH to min and see what temp the rads get to and also see what temp the temp gauge goes up to.

Its also helpful to note the temp on the gauge when it cuts out.

If the reset has been pressed more than about 15 times the calibration is afected downwards!

Tony

 

[BENRIBBANS]

I have put the stat on min so I will see what happens. It has been set to about 1/3 since this problem occured but all the rads are still too hot to touch, even one set to 2 on the TRV.

The temp gauge has never worked but BG said I will never need it so just left it, I guess I could get them to fix it as I am on contract with them? Presssure is at 1 bar.

I have pressed the cut out more than 15 times easily, probably about 5 or 6 times a day for the last few months! I am only leaning towards sludge as that is what the problem was last time, although a different fault - DHW not warming properly. The secondary heat exchanger was flushed and it has happened since. From what I have read in the manual, it says that the overheat stat must be replaced if the set temp is too low - so it might be that I need to replace the stat anyway if I have switched it back on a few hundred times....??

thanks
Ben

 

[BENRIBBANS]

ok, after turning the stat down - even the rads on 3-4 are hot to the touch. You can put your hand the top of the rad for maybe 3-4 seconds then it burns. The rads downstairs seem hotter than upstairs but not by much.

so what does this mean? not sludge?

Thanks
Ben

 

[gas4you]

Has the ch thermistor/ntc been checked/replaced. This would be my first port of call. The boiler could just be working on the overheat stat

Am I made of glass

Listen carefully, I will say this only 3 times

 

[BENRIBBANS]

sorry gas4you, did you say something...??

So how come the BG man didn't know this..?? What am I paying £14 a month for??!! I might cancel now.

If my understanding of the manual is correct, I need to replace the main circuit NTC which is on the LHS of the boiler? To do this I drain the boiler, change the NTC, refill the boiler and job done? How do I avoid air locks in the boiler? I presume I can re-fill with the mains tap with the bleed valve open until the water runs through then shut the bleed valve and mains tap?

Thanks again
Ben

 

[gas4you]

yes thats it.

As I am not in front of your boiler I cannot guarantee this is the problem, but it is certainly the cheapest and easiest thing to check and/or replace before any other decisions are taken further.

 

[BENRIBBANS]

Is there a way to check it first? Is there a resistance value it should have?

Thanks
Ben

 

[gas4you]

There will be, but without the MI's I could not tell you.

Agile's a mind of info like this though, so he will probably tell us later, or if not mehran will know.

 

[bengasman]

sorry gas4you, did you say something...??

So how come the BG man didn't know this..?? What am I paying £14 a month for??!! I might cancel now.

had you been reading posts on this forum, you would have canceled a long time ago