Biasi 24S No hot water from tap unless CH thermostat lit

[andy123456789012]

Well, it's been a while since I last posted on here.
This boiler is just so damn reliable really and it may need fixing again.

This is a common problem but I wonder if I can post enough detail here to get a one shot answer. I am almost fullly capable with a multimeter and I have the service manual.

However, I'm just wondering if I can avoid even taking the cover off etc.

The boiler was fully working in every aspect until one day it stopped delivering hot water. Listening to the boiler going when the thermostat is lit, it goes through a few noises, then finally a flame lit and central heating working.
If you turn on a hot water tap at this time, you will get hot water.
As soon as the boiler is turned off, the residual, heated water will go from hot to warm to cold.

Apart from that, everything else works.

So, obviously we have water flowing, we have gas igniting, we have water pumping, we have fan running and the flues/vents seem to be satisfactory according to the fact that the boiler is boiling.

In octoboer 2010 this boiler was revamped as detailed below from my 2010 final comment.

Finally, plumber was appointed for friday just gone, biasi specialist.
Changed flow diverter valve (don't know if diaphragm was a problem or not.)
Changed gas valve
and some other stuff inc service etc.

The system did not have any fluid replacements or maintenance except above.

 

[bolshy]

So, obviously we have water flowing, we have gas igniting, we have water pumping, we have fan running and the flues/vents seem to be satisfactory according to the fact that the boiler is boiling.

But it's not diverting properly. What exactly does it do when you open a hot tap with heating off?

 

[andy123456789012]

Hello Bolshy.
If I turn on a hot water tap whilst the central heating thermostat is off, I willl just get cold water.

 

[Agile]

Sounds like a failed DHW demand system!

Tony

 

[andy123456789012]

That's what I was thinking.

 

[bolshy]

If the boiler isn't registering a demand for DHW, it's likely the pressure switch is defective. I believe these boilers have a basic diaphragm operation, as many other makes do. Tony will put me straight if I'm incorrect here. You need to check whether the pin on the RHS of the diverter is moving out to make the switch when a HW tap is opened. If it is, then the switch is probably faulty. If not, then it's the diaphragm. Your manual is available online, and you don't need to open the combustion chamber for these checks. If you are competent with a multimeter, the instructions are in the manual. You could even check the switch has continuity when operated with the boiler off.
If you are out of your depth in any way, get a competent registered engineer in. Like Tony. He likes Biasi boilers. He may pass your way at some point in the near future.

 

[andy123456789012]

Anyway, we've had a bit of a rat issue and today I unscrewed the circuit board panels, discovering 2x 50g empty bags of cashew nuts. Ratty obviously liked the insulation value and had pulled them all the way into the accessible zones of the boiler.

It got them out of the kitchen sink cupboard bin one night and either carried them all the way underneath floorboards and through a small hole on the other side of the kitchen, but more likely took a more direct route, either tumble dryer bottom vent, which I thought was not 2 way trafficable, or simply pushed the cupboard doors apart and barged through down the nice accessible area down side of cupboard below boiler. Got a few stripped wires.

They like the neutral wires best or unplugged ones.

Anyway, I checked flow switch voltages for C/Heating and DomesticHotWater.
C/heating 11.84 volts, DHW 11.84 volts.

Hmm, so I went onto next phase and used a 1 inch inspection mirror plus removed side of boiler panel to check if microswitch was being pushed on dhw side. (nice clear plastic the microswitches are encapsulated in.

IT was being pushed so this validated the working (currently) of the diaphragm and diverter valve.

So, I got to work on removing the switch,just so I could play with it etc, expecting that I'd need to order a new microswitch or new block.

Anyway, after about 3minutes of navigation I noticed that the black wire was not present and had been chewed by the rat.(again, neutral or "currently" not live)

I replaced spade fitting onto shortened black wire and re-assembled the DHW switch assembly and locked it in place with spring metal fork.

Now we have hot water tap again.
Thoughts are
1) wonder how many other wires can be stripped in invisible locations or chewed, how this contributes to cross talk, interference etc.
2) Time to wire mesh the boiler top and bottom, without allowing any cross conduction of electricity potentials.
3) Damn rats
4) Damn rats
5) Watched a youtube video of pet rats, pretty cute things when domesticated.
6) Enough of this, I'm off to check traps etc.



Thanks for the helpful advice.

 

[bolshy]