Baxi 105e calling for dhw with no actual demand

[PaulMcgrath]

Hi,

I have a Baxi 105e and it appears to be calling for hot water most of the time even though there are no taps open.

What happens is the green tap light illuminates and the pump runs though the burner is not activated. The radiator in one of the bedrooms is absolutely roasting as well even though CH is not required.

If i turn off the boiler for 30 seconds and turn it back on again the unit reverts to normal however within a few days its back to how it was.

I suspected a faulty pcb which i have renewed however the fault is still there. I have read on this forum about the elusive sticky pin on the diverter valve diaphragm!! Could this be the cause and if so wouldn't the burner be firing all the time or would it be held off by the thermostat on the DHW?? If it is the pin whats the fix?? I'm an electrician by trade so go easy on me mechanical comrades.

Many thanks in advance.

Paul McGrath

 

[durhamplumber]

suspected a faulty pcb which i have renewed however the fault is still there. I have read on this forum about the elusive sticky pin on the diverter valve diaphragm!! Could this be the cause and if so wouldn't the burner be firing all the time or would it be held off by the thermostat on the DHW?? If it is the pin whats the fix?? I'm an electrician by trade so go easy on me mechanical comrades.

The most common cause of no hot water is the large diaphragm.That does not seem right in your case. Divertor valve probs more likely,as you say..Either new valve,or take to bits and fit the kit you can buy.Could be other things though,You might have put more faults on,depending on where you purchased the pcb.They are good boilers,worth repairing

 

[dilalio]

Trying to figure out why op has a roasting hot rad but says boiler not firing!

 

[undertrained]

It suggested to me your preheat is active (turned on) and diverter is stuck sending the heated water through your bedroom rad.

 

[ianmcd]

It suggested to me your preheat is active (turned on) and diverter is stuck sending the heated water through your bedroom rad.

If the boiler is as stated a Baxi 105 E then it wont have DHW pre heat, if it is the 105E instant , it will have a pre heat and could very well be the fault along with a passsing diverter valve

 

[undertrained]

If no preheat, then have you any dripping taps?

 

[PaulMcgrath]

Hi Guys,
Ta for the responses, to be clear, the boiler is firing and getting to temp, at times the pump doesn't appear to be shutting down and can run continuously all night and day if allowed. The pump appears to be running through hot water demand as the tap icon is lit. I'm guessing the burner isn't firing because the stat is holding the burner off because the water is at the correct temp. If the water temp drops, the burner appears to fire. For clarity its a 105 with pre heat and to make life even easier (NOT) i had it installed in the loft acess is difficult at best, so the radiators that get roasting are the bedrooms.
Fault is exactly the same as with the old pcb which i got online with a 12 month warranty.
I suspected a sticking relay within the pcb as the system resets when the boiler is electrically isolated for 30 secs which is why i replaced it but its exactly the same so i suspect its whatever is calling for the pump to run.
Just trying to work out a) whats causing the pump to run, b) why the rads would be red hot if the demand is for Hot water and not heating and c) hopefully what the fix is .
From reading the comments I'm surmising that there is a plunger (excuse terminology) within the diverter valve that pushes against the diaphragm and 'calls' for heat to the pcb which starts the pump and if necessary fires the boiler if there is a requirement via the water temp sensors? I'm guessing that if i were to pull the cable off the end switch then if this assembly was faulty then the call for hot water would cease??
If this component is faulty, is there a service kit?

Once again, thanks a lot for the assistance.

 

[ianmcd]

OK firstly you have told us the wrong boiler you have a 105 E INSTANT, not a 105E they are different, have look at the DHW priority microswitch and remove one of the spades and if the boiler stops false firing that is your problem,either the micro switch is causing a demand when there is none or your boiler has built in frost protection which is activated by the thermistors I would change both thermistors, easily changed and not expensive.

 

[durhamplumber]

OK firstly you have told us the wrong boiler you have a 105 E INSTANT, no

Ahhhhh...as said,,,,makes a big difference!!Well done diynot CID for sussing that out!