Another Baxi 105e with a problem.

[soops]

Hi,

I seem to be another one with the perrenially failing Baxi 105e.The problem with mine is as follows.

When the DHW is turned on (upstairs or downstairs, it makes no odds), the boiler will fire up, the water coming from the tap gets warm then as soon as it starts to come out of the tap with a bit of steam then the boiler shuts off.

After about 5-10 seconds of water running through then the boiler will kick up again and the cycle repeats.

If I close the tap down to about 1/3rd so it's a heavy trickle then it doesn't shut off and then we can gradually fill the bath or sink.

We have had the diverter valve changed, the big diapragm to the front of the diverter unit has also been swapped, the thermistor and the PCB, after the diverter had been changed it seemed a little better but has now gone back to how it was.

Any ideas as to what it can be? I wondered if it was the pump gobbed up but the DHW doesn't use the pump does it?

Someone please throw us a bone cos I dunna have a clue?

I don't do the work on it myself, a mate who is a plumber but doesn't normally do maintenance work just big installations is the one who opens up the boiler but he is stumped too and doesn't want to just keep changing parts for the sake of it as it is getting pretty expensive.

Thanks for your help in advance

 

[Terry7556]

have you cleaned the plate heat exchanger? or considered replacing it

 

[soops]

have you cleaned the plate heat exchanger? or considered replacing it

Before changing anything he gave it a service just to make sure that there wasn't anything obvious.

One of the things he mentioned that could be one of the next steps was to pull out the heat exchanger and flush it out in case it could be blocked.

Is this a serious contender for our possible problem? I'm a newb when it comes to these things so how could that be a problem? Is this the part that's buried right in the bowels of the boiler and you need to strip half of it out to get to it?

Thanks for the reply and I hope you can enlighten some more.

Cheers.

 

[DP]

105 is a solid boiler. Problems you describe are most likely due to lack of proper service and maintainance and primary water quality.

Before you get upset at what I have said, look at the boiler manual and read what it says should be done during a service and at what regularity. If system water is dirty, it will kill any boiler, not just yours.

 

[soops]

LOL, no worries DP. It just seems that the 105 when something goes wrong doesn't always come out as what the manual or the Baxi tech helpline says it is.

It's always followed a yearly service schedule as per the manual(pages 26 & 27). There's no problem with the actual water flow as the taps can be turned on full and there's quite a blast.

As for water quality we are on the Notts/Derby border and we are quite lucky as as it's on the soft side of normal, we don't even get any scale in the kettle!

Looks like the next step may be as Terence suggested and pulling it all to bits to gain access to the plate heat exchanger and see if that's blocked or damaged in some way.

Ta for the input, any help appreciated.

 

[mysteryman]

This looks like an internal circulation problem. If the primary side of the plate heat exchanger is obstructed, the remedy is a complete powerflush. Just changing a dirty plate heat ex merely relieves some of the symptoms, it does not cure the disease - sludge.

However, it could still be a diaphragm problem.

 

[namsag]

Absolute nonsense blocked plate would not require a power flush. The water ways are that small any little bit of carp blocks them always the temp within them can create its own scale etc.

With system completly cold turn on your hot tap and feel the 22mmm lefthand pipe under boiler if this gets hot you know the divertor is passing and so not all heat is going to the plate to heat up water .




It could also be a poorly set up gas valve and the min pressure is too high to stop proper modulation of the burner/ or a faulty HW sensor.

If not its a faulty plate which cost about 50 quid and take minutes to fit

Diaphragm can be disregarded if green demand light stays on

 

[soops]

Thanks for the replies and advice.

He's going to come and pullout the exchanger and see how badly it's blocked.

Time to get some calgon or cillit bang and give it a soak then.

Thanks again.