Baxi 105e Instant - no hot water

[CrewCab]

First post here so hello every one

I've a problem with out boiler, it's a Baxi 105e Instant, probably about 5 years old, been fairly regularly serviced. A couple of months ago it started producing no hot water other than that stored by the pre-heat function, does the same with CH on or off, CH works fine.

Regular plumber we have used for a long time has retired and moved away Had someone else in to have a look, ............ and he went away scratching his head.

Now I've been involved with the building trade all my working life and can certainly find my way around the basics, so at least if I can understand what the problem might be I should be able to find someone who can get it sorted.

The diverter valve push rods both actuate, as does the diverter head push rod, the dhw sensor seems to have the correct resistance, which falls as it gets hotter; the micro switch on the dhw valve is making contact when it's supposed to. All the neon's light correctly and no flashing (warning) lights.

When you turn on hot water the burner ignites as if to heat the water, it will go out after a short while, most likely as the water is going nowhere and getting too hot, then ignite again ........... etc

It clearly seems somewhere water is not being diverted into the dhw circuit, but as far as I can see all the controls are doing what they should be ................... to be fair I can see why the guy said "I don't know" and at least I prefer that answer to someone swapping loads of bit's just in case.

Sorry for the long rambling post, any idea's gratefully received.

Dave

 

[mspandh]

First post here so hello every one

I've a problem with out boiler, it's a Baxi 105e Instant, probably about 5 years old, been fairly regularly serviced. A couple of months ago it started producing no hot water other than that stored by the pre-heat function, does the same with CH on or off, CH works fine.

Regular plumber we have used for a long time has retired and moved away Had someone else in to have a look, ............ and he went away scratching his head.

Now I've been involved with the building trade all my working life and can certainly find my way around the basics, so at least if I can understand what the problem might be I should be able to find someone who can get it sorted.

The diverter valve push rods both actuate, as does the diverter head push rod, the dhw sensor seems to have the correct resistance, which falls as it gets hotter; the micro switch on the dhw valve is making contact when it's supposed to. All the neon's light correctly and no flashing (warning) lights.

When you turn on hot water the burner ignites as if to heat the water, it will go out after a short while, most likely as the water is going nowhere and getting too hot, then ignite again ........... etc

It clearly seems somewhere water is not being diverted into the dhw circuit, but as far as I can see all the controls are doing what they should be ................... to be fair I can see why the guy said "I don't know" and at least I prefer that answer to someone swapping loads of bit's just in case.

Sorry for the long rambling post, any idea's gratefully received.

Dave

May be a problem with the air pressure switch or fan.

 

[Rob]

If Ch works fine then its most likely a blockage in the Plate heat exchanger.

Assuming the diverter isnt stuck in CH mode there isnt alot else it can be.

 

[CrewCab]

Assuming the diverter isnt stuck in CH mode there isnt alot else it can be.

Thanks for that, stripped the Pressure Differential Assembly and the piston inside the unit was stuck ................ sorted now though.

Plate heat exchanger was fine, as were the diaphragms, but 2 new ones installed while it was stripped.

Thanks for pointing me in the right direction guys.

Dave

 

[baxpoti]

The diverter valve push rods both actuate, as does the diverter head push rod, .......... the micro switch on the dhw valve is making contact when it's supposed to.

Contradiction to your findings then?

 

[CrewCab]

Contradiction to your findings then?

Well I'm blooming sure the push rod which activates the micro switch was moving, must admit I've been scratching mi' head since and thinking "How" ........ but .......... the inner one. which was stuck, is in the body of the valve, where the red line is on the diagram below.

Dave

 

[Vic Spanner]

Well I'm blooming sure the push rod which activates the micro switch was moving, must admit I've been scratching mi' head since and thinking "How" ........ but .......... the inner one. which was stuck, is in the body of the valve, where the red line is on the diagram below.

Correct and well done.

 

[haveagodiyer]

Thanks Crewcab. Great diagram and was eactly the same problem I had on my 105e. Cleared crap around inner pin which then released. Hot water now restored.

 

[45yearsagasman]

 

[Agile]

In most of this style of boiler the rod you see which activates the microswitch is a different piece of rod from the one further back which is pushed forward by a spring.

So the front pin can come out but the rear one can still be jammed and not follow it.

Tony