Biasi 24S hot water too hot

[UnclePip]

I have a problem with my boiler the Ch works ok but when running the HW I get a reasonable flow rate but it gets too hot. The temp gauge on the boiler goes up to over 100! and then the cut out button pops out. This happens before I can fill the kitchen sink.

I had an engineer here today, he says that I need a new main circuit board which will cost over £400 and that I should cut my losses and fit a new boiler. £2000 !!!!

I had a quick google and seems to me that the heat exchanger might be blocked. Do you think this is likely? Or is it even simpler like a bust thermistor? Presumably the boiler modulates when heating the water?

I found the circuit board available for £120 and even cheaper on ebay. So I think that I am being overcharged. The boiler is about 8 years old.

Anyone know a good plumber in Bristol?

 

[Agile]

Let the boiler cool for a couple of hours and measure the resistance of each sensor. Should be about 13k.

Most likely the HW sensor is o/c.

Most unlikely to be the PCB.

You have an engineer who cannot fix boilers, quotes excessive price and expects you to pay over the odds for a new boiler when all it needs is an £18 sensor!

Tony Glazier

 

[bengasman]

...I had an engineer here today, he says that I need a new main circuit board which will cost over £400 and that I should cut my losses and fit a new boiler. £2000 !!!!

Nonsense, cowboy talk. 99% of boiler problems are economically viable to repair; my whole business is based on this principle. Look at my website if you want more info on repairs.

I had a quick google and seems to me that the heat exchanger might be blocked. Do you think this is likely?

No, only a small chance it's the pcb, and no chance it's a blocked hex

 

[UnclePip]

Thanks for the help.

I had a look inside and found that one of the thermistors was unplugged, So I thought that it was as simple as that, but it turned out not to be,, the boiler still got hotter and hotter. By turning off all but one of the rads I also found out that it does overheat on the CH as well.

I checked the themisors with a multimeter as per the service instructions and they were fine. So I went to the spares supplier around the corner and bought a new PCB, £144 including VAT, no doubt the professionals would have got it cheaper, anyway all working now.

Thanks for the advice, just pleased it was nothing to do with the gas side of things.

 

[vp1862]

Hi everyone, I am aware this is an old post but I have a biasi boiler and had the exact same issue so thought I would add my solution to the end of this thread for the greater good of DIY!

Mine is a m96.28 from 2008, and the boiler has a modulation valve along with the main on off solenoid. The modulator has a max and min gas pressure adjustment screw (hidden behind a clear plastic cap), and I am not sure whether my installer completely forgot to set these but the boiler was not able to set the gas pressure low enough to avoid the hot water overshooting the desired flow and dhw temperatures after a few minutes.

The service manual is completely useless in this regard as it points you directly to a faulty main board if the boiler can't modulate hot water. To rule out a board failure, get a multimeter and wedge the probes into the modulator coil connections (yellow and grey on mine) and with the boiler cold, monitor the voltage when you turn a hot tap on and move the dhw knob around on the front of the boiler. If the board is fine this will have a 1.6 - 14ish volts indicated, and this will show that any issue is probably a badly adjusted min gas setting. I turned mine (the tiny hex on the end) 2 whole turns anti clockwise and my hot water is now able to hold itself at 35 degrees C in 15 degree ambient. Adjusting this yourself without knowing the risks is dangerous so get your gas safe engineer to do it.

I sprayed a bit of soapy water around the adjuster (with the power off) to check for any leaks after disturbing the valve.

I hope this helps everyone! I was very glad it was a simple fix and I didn't need a new board. I guess as the ambient gets up to 25-30c it may need to be set further down but I'll cross that bridge when I come to it!