BAXI COMBI BOILER 105HE heating and water problems, switches off.

[PEPlumbing]

[h=2]

BAXI COMBI BOILER 105HE heating and water problems, switches off.[/h]

Hi, any ideas on this would be welcome.
I am at present trying to find fault with a Baxi Combi 105E Boiler.
Heating and hot water come on when both switches are on, however if I switch it over to just hot water the boiler instantly cuts out, EVERY time. Any suggestions??
So far I have changed the diaphragm, the diverter valve, the hot water temp sensor and the microswitch, checked that the pins touch and are out/in far enough, to no avail!!!
Still has made no difference at all, keeps cutting out. The red light flickers on the front - the tap 70 light.
The only thing I can see left to change is the PCB, however wondered if anybody else has any suggestions or come across this situation?​

 

[REDSAW]

plate heat exchanger is blocked.

 

[PEPlumbing]

Hi,
How can you tell if the heat exchanger is blocked??

As suggested by various other sources/Plumbers, so far have changed the following with new;-
Hot Water Temp Sensor
Diaphragm
Diverter Valve
Pump
Heat Exchanger
PCB
STILL having exactly the same problem, DHW switches off/boiler off when manually changed from CH and HW to JUST HW!!!!!!!!!
Pulling hair out now !!!!

 

[diamondgas]

You can tell Plate hex coz you'll see the temp on the front rise rapidly and the burner shut off yet water not hot enough .... Check temp diff between hot and cold taps. a good p-hex will supply the 35 degC rise as per mi's!

When you switch to hot water only does the boiler light for any period of time?

 

[Billy Bob Bob]

You can tell Plate hex coz you'll see the temp on the front rise rapidly and the burner shut off yet water not hot enough .... Check temp diff between hot and cold taps. a good p-hex will supply the 35 degC rise as per mi's!

When you switch to hot water only does the boiler light for any period of time?

good advice from steve and redsaw,another clue may be the flow to heating gets very,vert hot in dhw mode,on he versions of this boiler a failing aps will also give varying strange symptoms, you may get heating-no dhw or fire-lock out and so on alternitivly it may just die compleatly i take it your a installer new to break downs or just not familiar with the 105 boiler?

 

[diamondgas]

good advice from steve and redsaw,another clue may be the flow to heating gets very,vert hot in dhw mode,on he versions of this boiler a failing aps will also give varying strange symptoms, you may get heating-no dhw or fire-lock out and so on alternitivly it may just die compleatly i take it your a installer new to break downs or just not familiar with the 105 boiler?

Cheers matey 🙂 I wouldn't like to be the custard paying for this one :rofl:

 

[PEPlumbing]

No boiler does not light at all, immediately switches off.
Boiler does not fire up with just the hot water on therefore cannot see the temperature rise.!!

 

[PEPlumbing]

Would the hot water temp sensor stop the boiler firing up?

 

[Billy Bob Bob]

Would the hot water temp sensor stop the boiler firing up?

no whats its resistance?

 

[diamondgas]

Would the hot water temp sensor stop the boiler firing up?

You've replaced it yeh? ... Is your boiler the 105HE or 105e? Mechanical or electronic diverter valve? I'm a bit confused as to what appliance you are talking about my friend 🙂

 

[PEPlumbing]

Hi Steve it has been replaced and the model is the 105e.

 

[PEPlumbing]

Hi Steve, sorry the CH temp sensor has been replaced not the Hot water - do you think this could be the problem? Should i change the Hot water sensor and would it make any difference???

 

[diamondgas]

Well if the hot water sensor is at fault it can shut the boiler off prematurely. You would get the sensor fault light 70deg flashing .. didn't you mention that b4? Measure the resistance across the terminals of the sensor. Should be around 11kohms cold, reducing when heated.

Just a thought... Have you checked the control knob spindle into the pcb? If it's snapped then you can turn the front dial up to whatever you wish and it'll make no difference. Not sure if this is common on the 105e but have known of it on other boilers ! good luck 🙂