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

[clf-gas]

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

Thanks
Ben

12000ohms @ 20'c
1000ohms @ 100'c

 

[Agile]

There is a minor problem that sometimes an NTC only goes open circuit when it gets hot but....

An early posting by the OP said the boiler does cycle the burner on/off during the heating periods. That implies that the NTC does have some resistance otherwise the boiler would just overheat or reach an equilibrium.

Of course the resistance may be too high although thats very unusual.

The other possibility is that the PCB is not correctly reading the NTC value but again thats rare too.

The key is to let the boiler go cold and then measure the NTCs. They should both be around 10K.

Tony

 

[BENRIBBANS]

ok some more info, I have just sat next to the boiler for the last hour and monitored what happens;

Both NTC's read 10k at cool temp.
With CH pot on full a whistle can be heard coming from the main heat exchanger. At 1/3, the whistle disappears.
All rads set to 3 on TRV's. All rads hot to touch within 25 mins of CH being on. Boiler stays on full until it cuts out, it doesnt not ignite on/off as I previously said.
Flame is a yello/blue colour.
After 30mins, the whistling in the main heat exchanger comes back intermitently.
After 1 hour the boiler cut out. Both NTC's read 1.2k which I believe corresponds to 95 Deg C. After cut out a fizzing noise can be heard around the pump area.
All rads set to 1 on TRV's, CH pot on min, boiler cut out within 2 mins.

I will wait until it cools completely and see what the NTC's return to and also see if setting the rads to 1 makes any difference. So what else could it be other than the NTC's?

Thanks
Ben

 

[BENRIBBANS]

Tried running boiler after cooling down for an hour with all rads set to 1 on TRV's. Boiler cut out within 2 mins. Set all rads back to 4 on TRV's and boiler ran for an hour or so as before....??

Not sure what this means..??

Thanks
Ben

 

[gas4you]

Still sounds as it is overheating and ntc failing. But without being there and testing it is hard to be certain.

Can you quickly test the ntc just as the boiler has cut out?

 

[BENRIBBANS]

I could test it right after cut out, I guess I would be looking for open circuit? What else should I look for for NTC failure?

I have bought a new NTC today anyway, I thought if it isnt that I could take it back. I could fit it and see what difference it makes?

Thanks for your help
Ben

 

[Agile]

I still dont know what you mean by "cuts out" !

When the CH is on, does the flame reduce in size if you turn the CH temperature knob down?

Does the flame go out if you turn the CH knob down further?

Does it then stay off for 3-4 minutes?

Tony

 

[BENRIBBANS]

By cut out I mean the overheat stat, the small red push in switch.

By turning the CH knob down, the flames dont reduce. On min the flames are still 2-3 inches high and remain that way until the boiler over heats and cuts out.

 

[Deleted member 105431]

Have you tried leaving 1 trv head off to act as a bypass for the pump overrun?

 

[Deleted member 105431]

By cut out I mean the overheat stat, the small red push in switch.

By turning the CH knob down, the flames dont reduce. On min the flames are still 2-3 inches high and remain that way until the boiler over heats and cuts out.

then perhaps its a modulation fault. pcb/ntc/modureg coil. (or incorrectly set gv)

 

[Agile]

OK run the CH and then pull one wire off the gas valve green coil and see what happens to the flame size.

Then I will tell you whats wrong with it!

Tony

 

[BENRIBBANS]

just switched the CH heating after it being off for 3-4 hours. Fired up fine, pulled the green wire off the green gas vavle - no change in flame height. Pulled the black wire off - no change in flame height.

 

[BENRIBBANS]

As per the manual, I have tested the gas valve modulation coil resistance.

Across the green and black wire terminals of the main coil the resistance is 125 ohm - as per the manual.

The upper ON-OFF operator is 1500 ohm (manual says approx. 1260 ohms) and the lower ON-OFF operator is 3120 ohm (manual says approx. 3000 ohms). These values dont seem miles off but could this be the fault? New gas valve? And if this is the fault how do I convince BG that they need to change it??!! This is not a cheap part......

Thanks
Ben

 

[Agile]

There is nothing wrong with the gas valve itself.

However the flame size should fall to very small when you disconnect the mod coil.

I am forced to conclude that the gas valve is not set up correctly ( based on what you have told me! )

Unfortunately I cannot continue with any further fault rectification on an open forum as you are not CORGI registered.

Maybe I have lost track of the involvement by British Gas but if you had a CORGI person there I could explain on the phone what he needs to do.

Tony

 

[clf-gas]

Come on Tony he as told you what hes done, now what is wrong with it.

Im losing confidence in you