Baxi Combi 105e - New Heat Exchanger?

[Adam75]

Hi

I've got a Baxi Combi 105e and about 2 months ago was getting the hot water issue, the how water got warm, then cold, then warm etc.

Eventually the water would not get hot at all. The hot water light on the boiler came on when the taps were turned on, the boiler would then try to ignite but fail & one of the LEDs would flash.

So I cleaned the heat exchanger (the one at the bottom of the boiler, not sure if this is the primary or secondary?) which resolved the problem.

A couple of week back this started all over again so last weekend I cleaned it again and there was hardly any scum. The hot water worked ok in the week.

Today, no hot water. The boiler tries to ignite, fails, led flashes.

The central heating is fine.

Do I need a new heat exchanger or is there anything else I can check first?

Thanks
Adam

 

[DP]

It is the muck in the system that is the root cause of your problem.

Chemical cleanse might be the answer

 

[Agile]

Hi

A couple of week back this started all over again so last weekend I cleaned it again and there was hardly any scum. The hot water worked ok in the week.

Today, no hot water. The boiler tries to ignite, fails, led flashes.

The central heating is fine.

Thanks
Adam

Based on what you have said there then I would be suspecting a gas setting issue but for that you will need a competent gas reg boiler engineer.

An issue with dirt would only become apparent after the boiler has ignited.

It is a slightly unusual fault and could always be a PCB issue.

However, what I am saying is based on YOUR statement that the boiler trys and then fails to ignite. That may not really be the case!

Engineer time?

Tony

 

[Adam75]

Thanks DP & Agile. I hope its not the PCB as I changed that back in June.

Not sure what to do next, maybe you are right its time to call an engineer as the problem is intermittent.

We've had some hot water today, the boiler fires fine & the water stays hot then next time we turn the taps the LED comes on and the boiler fails to ignite!

And sometimes it struggles to ignite, LED warning light comes on but then finally it ignites as per the video below (apologises for the sideways video!)

http://youtu.be/SIeF6sKZnYU

Is it worth chemical cleaning the heating system? If so any one recommend any good chemicals?

Thanks

 

[Agile]

I dont see sludge as relevant so dont think thats going to help.

Whats the caption under the second LED which flashes at first and then finally goes out?

Tony

 

[gaswizzard]

Whats the caption under the second LED which flashes at first and then finally goes out?

Tony

HW sensor.

 

[Agile]

Hi

Eventually the water would not get hot at all. The hot water light on the boiler came on when the taps were turned on, the boiler would then try to ignite but fail & one of the LEDs would flash.

Thanks
Adam

They dont flash for fun!

Which one flashes when it fails to light?

G-W if thats the DHW flow switch light then is it normal for it to go out when the boiler lights as it seems to in the video?

We have been focussing on plate HE aspects as mentioned by the OP. But a very common failure is with the DHW demand switch although there is no evidence thats causing any problems. Even so I would probably have electrically checked its NO and NC contact resistances.

Tony

 

[Adam75]

The led that flashes then goes out is the tap with a line through it.

The dhw micro switch seems ok as when the push rod comes out the dhw led lights up straight away.

Thanks
Adam

 

[Adam75]

Just tried to run a bath, the boiler ignites and the first three LEDs light up (50C) then it goes out & the hot water led flashes again. It reignites and does the same thing over and over again!

I think I'm going to try replacing the hot water sensor

 

[gaswizzard]

G-W if thats the DHW flow switch light then is it normal for it to go out when the boiler lights as it seems to in the video?

The neon flashing is a FAULT light 'suggesting' faulty DHW thermistor..

 

[Adam75]

'suggesting', interesting word!

I swapped over the CH & DHW sensor cables, we got warm water (not hot enough for a bath) but the boiler did not go out. The CH did not work though.

Not really sure what this tells me!

 

[Agile]

It tells you that the DHW sensor is faulty.

You produced a viable sensor for DHW by swapping and had the faulty one for CH !

Most boilers still need some CH sensing when on DHW so you cannot assume that will also test OK. They also can be intermittent as I think yours is. Goes O/C when hot!

A simple test is to add a 10k resistor across the NTC in circuit.

Now G-W do you remember which sensor makes you wet?

Tony

 

[Adam75]

Thanks tony, look like I'll be getting a new sensor tomorrow.

The only thing I don't understand us why the faulty light does not flash all the time? It only flashes after running the dhw or when you disconnect it

 

[gaswizzard]

Now G-W do you remember which sensor makes you wet?

Tony

Yea both.