Biasi 424s - erratic

[steviebobs]

Hi all

Sorry to repost but better info this time.

Above boiler initially seemed to be cycling ( 20 secs on/150 secs off) on CH quarter thermo setting.

Boiler would fire, temp lights go to 60 degrees, boiler stops, temp lights go back down to 40 degrees within seconds.

Bloke at Biasi suggested CH probe. Changed - but does the same.

Now noticed another symptom. After running CH on high therm setting (3 quarters to full), after running DHW for shower for 5/10 mins, CH appears to be reluctant to come back on.

Now starting to suspect Diverter/Diaphragm.

Help?

SBobs

 

[Agile]

Savio 424S !

Its similar to the Biasi 24s but has a row of LEDs to indicate temperature and a transducer to show system pressure on LEDs.

It sounds to me as if the 4th DIP switch on the PCB may have been wrongly left in the anti cycle defeat position. It should have a 3-4 minute delay before CH fires up after going off on the temperature satisfied mode. The PCB is quite tricky to access though.

It almost makes me wonder if its been opened and the control knob spindles refitted wrongly ??? They can be fitted 180* out !

If the PCB has definately not been tampered with then its probably some flow restriction on the CH circuit. A boiler engineer would monitor the temperature against time on the circuit to judge the flow.

I dont see how the diverter could be involved if the DHW delivery is correct!

Tony Glazier

 

[steviebobs]

Agile

Great Points !

Been reading the manual and dont expect any probs to check your points - I will report back - Thanks again.

SBobs

 

[steviebobs]

Tony Agile Glazier

Again thanks for your comments - I have checked items and pot spindles are correctly 'aligned' and the four dip switched are all on.

Incidentally, I noticed on one of your previous replies to another problem, that you regerred to the Riac. pot. On my boiler this is set at max clockwise. On the others you suggested it should be max anti-clock, but not necessaily on this boiler.

Also. These settings would all have been done when commisioned in 1998-ish

Regards

Steve

 

[Agile]

I hope you mean "on" as closest to the control spindles.

The "Risc" is the CH power setting. My other comment was in relation to the M90 32 kW.

If you have got about 5-8 rads then about 30% up from the minimum ( anticlockwise would be about right ).

Just that may improve your problem.

If you turn on DHW and pull off one of the wires to the green coil on the gas valve then the flame should die down to a small size. e.g. from 50 mm high to 10 mm but these are just an approximation. That implies the gas valve is set up reasonably correctly.

Tony Glazier

 

[steviebobs]

Tony

Thanks yet again!

1. dips as you suggest - all at 'spindle side

2. 13 rads, mostly 72 X 24, but three 36 X 24 or less. No recent changes.

3. Will try the gas valve/ flame size and report back !

Steve

 

[Agile]

With 13 cold rads set the "risc" to about HALF the maximum flame size erring on the low side!

It might be worth checking the maximum power setting. If you can set the tap flow rate to 9.4 litres per second then the water temperature should be raised about 35*C.

Tony

 

[steviebobs]

Tony

Reduced the Risc from max to half, but heating just died with virtually cold rads, so put back to original max setting.

Let me give today's summary! It is becoming quite typical.

1. Boiler came on at 0630 (CH Therm set to half) - heated up fine
2. Couple of quick showers by 0830, still going fine - house warmed up nice, Rads hot, now about 1130.
3. My son then does his thing for national cleanliness by spending 20 mins in shower - heating obviously takes second place for those 20 mins.
4. After his shower, system never gets hot again. Burner lights, stays on high flame for 3/4 seconds, drops to low flame for 20 seconds, then turns off leaving flashing 'boiler on' led. 3 mins later, fires up and repeats the cycle.

Rads stay only warm although CH stat still on half. During this cycle, the temp leds go from 40 to 70 and (back to 40 again quickly when burner goes off).

Incidentally, I have just turned the whole thing off for half an hour, and when I turned back on, the burner lit, 3/4 secs on high flame, then lowers, temp leds go from 40 to 60 (Not 70) BUT, it doesnt switch off. Rads getting hot again.

Seems like it has gone back to normal operation again!

The trigger seems to have been drawing off significant DHW?


As a further aside, when I drained the main circuit ( to replace the CH probe initially), the drained water was nice and clear, so dont suspect sludging affecting main circuit flow, which, I thought, might be causing the burner to turn off prematurely.

Steve

 

[Agile]

The fault indicated by your description is that the diverter valve is not fully returning to the ( resting ) CH position.

I would still suggest that the "risc" setting should be half flame height as set with the rads cold but the front panel CH knob should be 3/4 up.

You can get an idea of whats happening by holding the CH flow pipe on the left, it should heat up to about 70*C after say 5-10 minutes if the diverter valve is fully open but much quicker if the diverter is mostly closed.

When its not working correctly you may be able to prompt it by opening a hot tap for just one second, ideally quickly, and that might encourage it to return fully.

If, with an inspection mirror and torch, you can see the pin which actuates the DHW flow switch ( behind the gas valve ) then it should move about 6-8 mm and retract promptly when DHW flow ceases.

When we have confirmed this is the problem then we can consider solutions.

Tony

 

[steviebobs]

Tony

Interesting stuff.

On the diverter valve, the 'main circuit flow switch' is on when the pump is, ie all the time, which makes sense as I guess thats whats it there to monitor.

The DHW flow switch activating rod fully depresses the microswitch with DHW flow, BUT, when the DHW is stopped, it appears to move a little way back, but I am guesing not fully. In this position, the rod is just resting on the microswitch lever - I dont believe enough to operate the microswitch - but its total movement from fully operational back to rest does not seem to be as much as the 6-8 mm as suggested.

It looks as if the activating rod could retreat further into the body of the valve.

If I am right, then you are, by suggesting tha the valve isnt fully going back over to CH after drawing DHW.

Incidentally, on CH, the flow pipe heats up very quickly and also cools down quickly after burner stops.

Regards

Steve

 

[Agile]

Now the interesting bits!

You have not said how many mm the pin retracts but lets assume thats the problem as its what the symptoms point towards.

The problem is probably associated with the left hand end.

You should isolate and drain the boiler circuit, loosen the two square brass screws about three turns and carefully withdraw the diaphragm unit to the left and then push it towards the back.

See if the pin in the diaphragm unit can be pushed back inside easily.

Next undo the left hand large gland nut on the diverter which contains the square screws and remove it together with the internal shuttle.

See if the flow switch pin has retracted fully at this point. If so the shuttle pin is probably dirty and neeeds to be cleaned and greased with silicone and reassembled. That may be all that is needed to fix it. If so reassemble and pressurise and test. This large gland might leak afterwards and have to be replaced in due course.

If the right hand DHW flow SW pin is still still not retracting then that will need to be taken out and checked and cleaned. The seal on the right hand shuttle could have swollen and become tight or the pin could be dirty. The gland might start leaking after the pin has been cleaned.

To access the RH pin it is necessary to remove the gas valve and I cannot give any advice on how to do that to anyone who is not CORGI registered.

You might have it working for Christmas!

Tony

 

[steviebobs]

Tony

.....You are my hero by the way...............

I understand all you say. I've just had a glass of wine, so may wait till tomorrow to do the necessary. But, all makes sense. Fortunately the weather is mild.

I would guess the DHW pin extracts about 4mm from full on (about the size of the microswitch 'dimple'), as the microswitch lever is still resting (lightly) on the dimple, but I am certain it is not keeping it operated.

The pin on the DHW one appears to have a line around it as if it has different 'normal' position to the one it has adopted of late. Maybe 2/3 mm toward the microswitch end

Just tried DHW off and on a few times and the pin does move pretty quick on and off, but still seems short of full return travel.

If it is done before Xmas then an Xmas drink is in order. Do you do 'the Wirral' often?

Thanks again - you obviously love your job - join the club.

Steve

 

[steviebobs]

Tont

Second post

We (You !) are on the right track here I suggest.

This morning all going fine (no big showers as yet) BUT the right hand DH pin has retracted much further and is much closer to the body of the diverter valve. So it certainly is sticking.

I will carry on with your instructions re your last post and if no luck then will get a Corgi person to remove gas valve and get the diverter sorted.

I realise that the DH pin is virtually inaccesible with the gas valve in the way !

Thanks again

Steve

 

[steviebobs]

Tony

All done and 48 hours to go !


Stripped the diverter, cleaned all bits, shuttle etc, greased and re-assembled.

Seems to be working perfectly ( now that the weather has got warmer....!!) Set CH stat on an eighth today and too warm ! Then again outside temp is 10+

The right hand pin now is fully retracted on CH and fully out on DHW so looks like 'jobs a good 'un.'

Thanks for all of your help - greatly appreciated.

Just one Q, educate me! Regarding the Risc setting, why would it have bneen set at max in the first place, and what is the logic of the correct setting in relation to the HD stat?

Regards again and have a good break - when it starts - and best wishes to you and yours.

Steve

 

[Agile]

You still need to set the "risc".

In the absence of any other information set it the the middle position and perhaps err on the lower ( anticlockwise ) position.

When a boiler is installed the CH output should be set to match the radiator output by the installer or commissioning engineer.

This setting becomes even more important with a condensing boiler! It is a sad reflection on our industry that very few are ever set at all and most are left on maximum. This means the boiler will be more noisy and less efficient!

I was able to diagnose this fellow's problems because he was able to describe his boiler's operation very clearly.

Happy Christmas to all.

Tony