105e instant..Any Baxi/Potty engineers/or anyone

[scatmanjohn]

Any help from anyone appreciated,

I went to a baxi 105e instant combi and quess what, it was working fine whilst i was there.

Customer says when they have the heating on it can suddenly just go off.
When they go to the boiler it is showing a demand for hot water (solid green light, not flashing).
They say by just resetting the boiler it returns to working correctly for a while.
Baxi tech help say its a sticking DHW flowswitch microswitch but i'm not too sure thats the fault.
To me, if the switch was sticking then resetting would not release the stuck switch.

Has anyone had a similar problem to this with the 105e instant.

Any thoughts much appreciated

 

[weargas]

Happens all the time. It isn't the dhw microswitch, its on the primary section behind the dhw diaphragm section. The clip can be removed from behind the dhw m/s and the whole section eased forward and out of the way without turning off the cold feed. Behind it is the removeable front section of what looks like a diverter valve but isn't as such. With the primary side drained you can remove this front tailplate section, clean and grease the pin and re-assemble. I use a tap spanner to get it off from the front but if you need to get something on it sideways you're gonna have to remove the r/h side panel, diverter actuator and it's better to remove the thermistor and limit stat in case of damage. I'll put money on it it isn't the dhw section.

 

[scatmanjohn]

Thanks for that weargas.

If that was the fault i don't think resetting the boiler would get it working normally again would it.

 

[Baxmax]

Possible P.C.B The Panacia of all things wrong....

 

[scatmanjohn]

Possible P.C.B The Panacia of all things wrong....

Thanks...have you come across this fault before.

I guess you may be a Baxi fella from your name.

 

[Agile]

I think that Weargas is referring to the system flow switch sticking.

Although I have not encountered that one yet it does sound feasible.

Tony

 

[scatmanjohn]

Tony...I can't see how that would show a demand for DHW.

I think weargas was talking about the hydraulic section behind the DHW flow valve. I think it diverts DHW into the expansion vessel during preheat. (not 100% without looking)

Thanks anyway

 

[weargas]

D'ya know, I've never given the instant any thoughts on what that section does (too lazy to follow the flow!). I'm not gonna be arrogant and pretend I know everything but maybe I'll take a look at it now I'm curious enough. It's just I've done many where the dhw microswitch doesn't return completely (matter of 1mm) because the pin in this section doesn't return. I must say however I can't see how resetting it would cure this unless the pump is helping to stop the pin returning. Which way does the water flow??? (I knew I should've found out about that section!!!)
I think you need to establish if the problem seems to occur after dhw use. Put the customer on LED watch after dhw use.

 

[Paul Barker]

I wondered where they got the "instant" storage. Cunning to employ the expansion vessel.

 

[Paul Barker]

I wondered where they got the "instant" storage. Cunning to employ the expansion vessel. Are you sure they don't just ensure that the plate heat secondary is constantly kept hot?

I don't know just musing.

 

[weargas]

That's it. The section behind the dhw flow switch section is the diverter valve operated hydraulically when a tap is turned on. The other diverter valve operated with an electronic actuator is the pre-heat diverter valve to keep that big old 32 plate heat ex hot. How needlessly complicated.
Damn you all for making me think so hard so early!!!

 

[Agile]

The manifold behind the diaphragm unit "follows" the diaphragm under the pressure of a spring in its base. Failure to "follow" is a common fault which catches out those who have changed just the diaphragm and then find it still does not work.

The other problem of the diverter not fully returning is less common but can be encountered.

This Baxi does sound to me as if it has a faulty switch which is activating when its not being pushed. To me a faulty switch is a common fault on these. The switch complete with leads is only about £14 but takes a few minutes to fit because you have to replace all these leads from the PCB. Its really a very cheap little switch and I have often wondered if a replacement with one from an Alpha 240 would be better but that would be non standard of course and we are expected to replace poor components with the same poor components!

Tony

 

[scatmanjohn]

weargas wrote:

I think you need to establish if the problem seems to occur after dhw use. Put the customer on LED watch after dhw use

Thats what i have done. I'm going back tomorrow and have told them not to reset in the morning if it does it. A least i will be able to see what it is doing that way.

Paul Barker wrote:

I wondered where they got the "instant" storage. Cunning to employ the expansion vessel. Are you sure they don't just ensure that the plate heat secondary is constantly kept hot?

I don't know just musing.

the expansion vessel is definately used in the preheat process. Have a look next time you work on one, its encased in polystyrene. I think the heated water that is stored in it is used as a ready supply of heated water which is used to heat the DHW "instantly"
Funny thing is that every one i have been to the customer has turned it off because it fires the boiler up every time the stored water cools down. So that means in the middle of the night as well.
Maybe a timed preheat would be a better idea.

Agile wrote

This Baxi does sound to me as if it has a faulty switch which is activating when its not being pushed

Thats what the Baxi tech help said as well but i can't get my head round it.

I am going back armed with a microswitch and will strip and clean the mentioned diverter.

Thanks one and all.

 

[lor]

paul barker , like many ideas it sounds very good ( to use pv to store but it had many failures . also vessel capacity is limited.canging the div valve on the instant is one of the hardestjobs ive done and ive done a few .

 

[scatmanjohn]

Just an update on this one...

Fit new microswitch wiring harness kit over a week ago and its been fine ever since.

By the way i took the old microswitch to bits and i am not suprised that they go faulty. What a poor design.

Thanks for everyones comments