Baxi 105e Combi Boiler fault

[electroman68]

Hi There,

I wondered whether anyone could shed any light on a fault with my boiler.

Basically, the boiler started making a loud noise yesterday when DHW was called for. CH is turned off at the moment due to mild weather. Anyway, the noise was like a loud buzzing/whirring type sound and it took longer than usual for hot water to come through the tap.

Since then the boiler had been working today without making the loud noise, although DHW was still taking an age to heat up.

Tonight, the boiler has stopped heating water up completely.

I looked at the LED's on the front panel and a few seconds after turning a hot tap on the 60 degree LED flashes on and off, which is the fault lamp for the Pump. Does this sound like the pump is knackered or could it indicate a problem elsewhere? The pilot light does not come on at all.

Hope someone can advise.

Thanks,
Robert.

 

[bazdaman]

Sounds like a sticking pump see faqs about checking pump

 

[electroman68]

Thanks for your reply. The pump is a grundfos. I did undo the bleed screw on top of the pump and a tiny amount of air was released. However, this still hasn't solved the problem so will check the pump as you suggested.

 

[electroman68]

Ok, I followed the FAQ regarding checking the pump as follows.

1. I set thermostat high to call for CH and ensured heating timer was on.

2. I removed the large chrome screw from the front of the pump.

3. I then switched the boiler on at the mains and the pump fired up and I could clearly see the spindle turning freely. However, after a few seconds the Pump fault LED started flashing again.

4. With everything as it is I turned the boiler off and then on again and this time turned on a tap to call for DHW. The pump again started spinning but this time the boiler fired up and heated the water with no fault led flashing.

5. At this point there was a steady drip of water coming out from the front of the pump. I then replaced the screw and tried the DHW again. It still appears to be working ok. However, if I try the CH again, the fault LED flashes after a few seconds.

For the record, the pressure was a little on the low side at just over 0.5 bar but I had refilled it to around 1 bar when cold earlier today.

Another interesting thing I noticed is that when I removed the vent screw from the top of the pump (small brass thumb screw) no water at all seeps out from it. I seem to recall that once all air has been removed then water should come out from here? If not then that's fine, but thought i'd mention this in case it's significant.

Anyway, the DHW at least is suddenly working again.

Thanks,
Robert.

 

[twgas]

If HW works every time I would suspect a blocked filter, in the return iso valve.

 

[electroman68]

UPDATE: Ok, so I used the shower this morning for between 5 and 10 minutes and could hear a loud noise from the boiler halfway through this period. The noise lasted for approx. 5 seconds and it sounded like a loud scraping type sound. The HW continued to work during this time, although it still takes longer than usual for the hot water to come through the taps.

Anyway, after this I used the hot tap on the bathroom sink and had this running for a couple of minutes. The water heated up and no strange noise could be heard from the boiler on this occasion.

It appears to be an intermittent problem and I'm wondering whether it also depends on the volume of water flow, hence why I heard it when the shower was running but not when the sink tap was running.

I'm not a boiler expert by any stretch but for some reason I keep thinking of the heat exchanger. I was told by a plumber some time back that this is likely to scale up at some point since we live in a hard water area.

Any further tips/advice would be most appreciated. Thanks everyone for your replies so far.

Robert.

 

[electroman68]

Hi again.

I read in the Baxi Service manual that the AAV on top of the pump is supposed to be left open by undoing the screw slightly.

For some time now this screw has been done up tight, until yesterday when I undid it to release the air. I did then close it again as it was done up before and I therefore assumed it should be done up again.

I am wondering whether this should be left open slightly or nipped up and also whether this could contribute towards the problems I am experiencing with the boiler?

Any thoughts on this would be most appreciated.

Also, I have recently turned the mains water stop cock off in order to replace a tap washer in the downstairs toilet sink and wonder if this could be related to the problem, i.e. trapped air in the system that could explain the loud scraping type noise and other issues mentioned previously?

Thanks,
Robert.

Thanks,
Robert.

 

[twgas]

If HW works every time I would suspect a blocked filter, in the return iso valve.

have you done this

 

[electroman68]

Hi Mick.

The problem is that the HW doesn't work all of the time, it seems to work most of the time.

Should I unscrew the AAV half a turn or so?

Thanks,
Robert.

 

[twgas]

The AAV should be slightly open but I dont believe that is the cause of your problem.
I'd still check the filter, even if its not blocked it may well give you an indication of the state of the system water.

 

[Gasguru]

The problem is the boiler primary flow switch is indicating a lack of primary water flow....

Check the switch resistance...the switch on top of the diverter.

Check the switch operates every time the pump runs.

If it doesn't the chances are it's a week pump (take the head off and feel the torque when it's running), partial blockage, or the primary flow sensor assembly is iffy.

Forget the return filter at this stage...it has nothing to do with the domestic hot water performance.

 

[electroman68]

Ok, thanks for that. I will check the flow switch. That's more my area of expertise being an Electronics Engineer!

If this tests ok I will then check the pump. I did check that the pump is running freely but have not yet checked the torque.

Incidentally, if the switch doesn't operate every time DHW is called for, could this also indicate a damaged diaphragm in the diverter valve or possibly even the push rod sticking?

Do you think that the loud scraping noise that can sometimes be heard when the hot water has been running for a while, could be due to a problem with scale. Could this indicate a problem with the Plate Heat Exchanger? Any easy way to verify this? Sorry for all the questions but just trying to get a better understanding of what's going on.

Interestingly, I have used the hot water twice this evening and both times it heated up fine and no loud noise could be heard from the boiler. Problem is definitely intermittent whatever it is.

Thanks for everyone's help so far.

 

[Gasguru]

As the pump is started the pin should rise up and activate the switch to prove there is sufficient water flow for the next firing up sequence...it's a safety device. Very rarely does the diaphragm perish or the pin stick. It's more likely an issue with a clogged impeller, low motor torque or partial blockage.

Take off the pump head, and check the impeller torque. Sometimes you find there is a reluctance to start..the start capacitor may have gone low. Don't worry about running the pump with no water surrounding it....should be fine for the brief testing time.

The noise could be the pump or the primary heat exchanger kettling due to poor flow.