Biasi 24S Problem

[newcomers]

hi guys,

went to a job just now, complaint was hot water not hot enough.

Got there, opened hot tap, and it was running warm, and only got hot when I slowed the flow rate.

I checked the burner pressure and it was only 6, and it sholudve been 10.

I removed 1 of the wires from the modulating coil from the gas valve, switched power back on and min pressure was ok.

Put the wire back on, and then the pressure wouodnt go above minimum, and now wont do so. I removed both wires from coil and measured the resistance across the wires and got OL, and when I measured the resistance across the coil the resitance was very high.

Basically, I dont know whether its the ignition board or the gas valve thats faulty. What do you guys think?

Thanks

 

[bengasman]

Pcb, as you probably know, can not be tested but valve can. Biasi manuals are pretty extensive though I don’t know if they tell you the resistance of the coil.
The valve has manual adjustment options though, 9mm spanner goes on the little hex on the spindle that is pointing to the left side of the boiler.
Some of the date is not in the main manual but in the A5 supplement.
Minimum pressure 1.5, ignition 6 and full on 9 if you want to stay on the safe side.
Min pressure adjuster is 6 or 7 mm spanner if I remember correctly.

 

[newcomers]

Trouble is I cant change any of the pressures because its just staying at the minimum

 

[bengasman]

bum bum bum bum bum
sounds like it's bummer

 

[newcomers]

bum bum bum bum bum
sounds like it's bummer

indeed!!!

i cant even eliminate the dhw h/e until i can get the pressures correct.

Think ill have to get ignition pcb and gas valve just in case

 

[Gasguru]

The min pressure is around 1.3 mbar, have you adjusted the gas valve setting or the burner pressure pot since you were originally getting 6 mbar on ignition.

The gas valve uses the Honeywell Combined Valve & Ignition module.

I've had similar faults whereby the boiler will ignite and stay at the ignition pressure (around 6mbar). Pins 1&2 (red/black wires) on the CVI module are a simple relay contacts that close to indicate to the main board that ignition has been successful. Not uncommon to find the CVI header connector solder joints are broken or other poor joints on the module thus the main board sits at the ignition pressure.

The modules do come apart...they are glued but careful prising is needed.

Top two pins on the gas valve should be around 1250 ohms

Lower two pins around 3000 ohms.

Never try to measure the resitance of the modualtor wires.

 

[newcomers]

The min pressure is around 1.3 mbar, have you adjusted the gas valve setting or the burner pressure pot since you were originally getting 6 mbar on ignition.

The gas valve uses the Honeywell Combined Valve & Ignition module.

I've had similar faults whereby the boiler will ignite and stay at the ignition pressure (around 6mbar). Pins 1&2 (red/black wires) on the CVI module are a simple relay contacts that close to indicate to the main board that ignition has been successful. Not uncommon to find the CVI header connector solder joints are broken or other poor joints on the module thus the main board sits at the ignition pressure.

The modules do come apart...they are glued but careful prising is needed.

Top two pins on the gas valve should be around 1250 ohms

Lower two pins around 3000 ohms.

Never try to measure the resitance of the modualtor wires.

whys that?

Im not getting 6mbar, im only getting 1.6 mbar

 

[Gasguru]

Originally you were getting a correct 6 mbar ignition pressure so what have you done for it now to only sit at the minimum pressure - have you reconnected the modulator coil wires? Are they broken at the crimped terminals?

You said you pulled off the mod wires and then measured the resistance across them. What will this prove? You could actually damage your multimeter since a charged capacitor could shove a sizeable current into your meter. Measure the voltage across the mod coil to give a useful reading.

Only use the resitance range to measure resistance of individual components ie cables, solenoids, fans, switch contacts etc.

 

[newcomers]

I took 1 lead of the coil to see min pressure which was correct. When I replaced the lead it didnt go back to 6mbar, just sat at minimum

When I check the resistance of the coil with the leads connected, I get OL. With leads disconnected, I get a high resistance reading across coil.

 

[Gasguru]

You never check the resistance of the coil with the leads connected...otherwise the components on the main board will be in parrallel with the mod coil giving a false reading.

The mod coil is about 125 ohms with the wires DISCONNECTED.

Voltage in the book is 16V DV (presumerably at maximum) when connected to the mod coil. Tony will know more.

Have you checked your meter is funtioning correctly, short the meter leads together and check you get <1ohm.

Are you sure you are using the meter correct? is it autoranging? I've not known a mod coil to fail on these but I've repaired loads of CVI modules.

 

[newcomers]

ok how do i check the cvi module?

 

[Gasguru]

Pulling apart the module can't be explained over a forum...it just involves a stanley knife and a bit of leverage

You need to work out why the burner is not stepping up to the 6mbar which it did before you started measuring. Were you taking resistance measurments across the mod coil while the boiler was fired up?

Have you adjusted the ignition pot on the main board or the max/min settings on the GV?

 

[newcomers]

didnt do anything electrical while the boiler was on

Yeah I tried adjusting the max pressure adjustment on gas valve but it made no difference. Did that while it was @ 6mbar

 

[Gasguru]

Remember the CVI module just controls the ignition and safety aspects of operation. 240V is fed to the module (pins 9&11) by the main board to enable ignition. The main board will set the mod coil voltage according to the preset ignition pressure setting. On ignition the burner pressure ramps up to 6 mbar. Once the flame has been proved pins 1&2 on the CVI module (either a simple relay or optocoupler) are sensed by the main board and the burner ramps then up to the required main burner pressure ie 10.5mbar if cold or lower if necessary.

I'm wondering if you have set the max adjustment out so far that the gas valve will not go higher then the min rate. I know from replacing these valves in the past it can take a fair amount of adjustment to get them back on track. Measure the voltage on the coil to ascertain you have the correct ignition voltage and then re-adjust the max setting to bring it back to 6 mbar. If the voltage doesn't rise from the ignition setting suspect the CVI module.

Hopefully Tony will be along and will tell us what voltages should be expected at min/ign and maximum settings. Otherwise Biasi tech.

 

[newcomers]

but evtn if i do manage to get it back to 6mb, i still have the problem of not going to 10mb