Biasi combi not calling for hot water

dave123456_2

Hi, my biasi combi has just this minute stopped working. The central heating side is fine, but the boiler isnt calling for hot water, obviously this will be a replacement part, any ideas would be great.

Best Regards.

Snow_Dog

Try cycling power to the boiler, it maybe the processor card has got its knickers in a twist. Leave the power off for a couple of minutes

When you run the hot tap does the boiler fire up?

It maybe you have a faulty thermal sensor indicating to the boiler that DHW is already at temperature.

dave123456_2

could you please explain what you mean by 'cycling power to the boiler', are you advising me to turn the power off to the boiler for a while, in hope that it may reset itself?
At present if the central heating is switched on the boiler will fire up, if the hot tap is turned on, the boiler will not fire to heat the water.

Snow_Dog

Cycling the power means turn off the electrical supply to the boiler (if that is easy to do, eg switch).

Modern boilers have more electronics in them than a 1980s sinclair computer and every now and then electronic circuits have a habit of getting their wires crossed as it were. Hence when your modem plays up or some other piece of kit the first thing the technical helpdesk will tell you to do is turn off for a couple of minutes and reboot.

In your case I dont think its that likely that cycling power will solve the problem, but its the first step in the fault finding process, try the simple to do things first.

From your description of the fault the most likely culprit is a faulty temperature sender on the DHW (domestic hot water) output, or possibly a faulty flow sensor. Most boilers are fitted with a flow sensor on the cold water in so that they signal to the boiler that when a tap is turned on the minimum water flow is going through the system and the boiler can fire up.

If this sensor is knackered then the boiler wont fire up for DHW. Those are the sort of failures I would expect. If yuo call in a good heating engineer he should be able to identify if its either of these sensors within a few minutes, 15 at tops if you include reading the manual to get where he has to probe for the correct signals.

The fact that the boiler is firing up for the heating would indicate the expensive to fix parts are OK, eg burners, fan, gas valve, etc.

If they try to blag first of all with a PCB replacement confirm they have checked the sensor outputs, and if you want to check PCB prices for your boiler google online boiler spares, they have an online database with prices.

dangermouse83

Hi dave,

Just read snow dog's post and agree. Hopefully it's just the diverter valve gone to pot.

My boiler's doing the same thing at the moment.

So the heating works.... I presume that you get hot water when the heating is on?

good luck with it!

roscar

dave123456 wrote: »

Hi, my biasi combi has just this minute stopped working. The central heating side is fine, but the boiler isnt calling for hot water, obviously this will be a replacement part, any ideas would be great.

Best Regards.

a common fault with no hot water on combi's is the diaphram, this is in the valve containing the ( diaphram rubber ) a circular disc that is put under pressure when the hot tap is turned on this in turn pushes on a micro switch which then gives power to fire up the boiler if the rubber is split the pressure bypasses therefore not pushing the micro switch hence not giving power to fire the boiler. if you are getting hot or warm water when you turn on the tap with the heating also running, a split diaphram is the more likely problem. hope this helps..kev

gary.harwood

try tapping pressurs switch? remove front cover & tap
pressure switch one with clear tube connected....?