Baxi Instant 80HE not detecting Hot Water Flow

Have have just renovated a house for my In-Laws and the last job (why did I put this off??) is the boiler.

I am coming here as Baxi give me snippits of help, but keep refusing to talk any more as I am not "Gas Safe", so I hope someone here might be able to help.

It has an Baxi Instant 80HE, which only intermittently detects HW flow... It works when I turn on the bath tap (lots of water), but not the sinks..

I have looked at the mechanism which detects flow, and its obvious what the issue is.. When I turn on the tap, the "pin" that presses the microswitch comes out long and hard.. But when I turn on the sink taps, it only comes out 1/2 way and I can easily push it back.

At the weekend I had a look at the diaphragm and associated mechanism and it was sound.. I cleaned of a bit of scale and it made little difference.

So then I moved onto the "Venturi" which was something that Baxi told me to look at. They said that sometimes the splines come off of the cage. So I removed the cartridge, and to my surprise, the Venturi was missing. I checked inside the opening with a mirror/torch and its not there. The Venturi is awol. (See attached photo)

So I would hope this could be the cause.. But a call to Baxi today resulted in them telling me that it WAS there as teh boiler wouldn't work at all without it. They refused to accept that in my case the venturi was missing.. And the boiler works some times and simply refused to speak to me.

Does anyone with Baxi knowledge know why my venturi is missing? And why the boiler still works??.

How confident are you that if I simply replace the venturi is will solve my problem?

Thanks in advance for any advice.. I need to get this fixed quickly now as they have moved in and have no reliable hot water, so don't have time on my side.

Jon

 

Cheers TT.. I am relieved by your answer as I got into a bit of hot water (See what I did there ) asking this on other forums, with Plumbers telling me that I am being irresponsible and illegal.

The house is 9 years old and this "fault" was there when we got the keys. I worked out what was wrong early on (i.e the push rod doesn't have enough torque/length to trigger the microswitch), but I put off the repair until now, which was a mistake.

I have checked the diaphragm and its fine.. And the push rods are clean and move freely...

So the last thing (based on what Baxi told me) is the Venturi and the fact that its missing has to be significant... I will get the new part in the coming days, so will have it fitted soon and hopefully that will be it.

On the tap front, I measured that they are chucking out 5L per minute, which is more then enough to trigger the boiler, so I don't think its got anything to do with flow..

Cheers

Jon

 

Cheers TT. I fully accept that playing around with boilers is illegal and could be dangerous.. But as you said, I am only touching the DHW side and would never touch the gas... Its also illegal to do your own electrics but I do that too.. And on that front I am entirly competant to do so (As an electronics engineer) and believe that any work I do would be to the standard of a pro.. But I fully understand why the laws are there as I have seen some unbelievable and shocking (I did it again, I am in pun heaven).

With my Venturi, I did use a mirror and torch and the chamber looked empty.. But before I put the new one in, I will certainly check and IF I can get a camera in there, will take a photo so I can really scrutinize it.

Your advice about the Diaphragm is valid and I will do just that..

THe parts should be here this week, so fingers crossed!

Jon

 

Just to give an update and closure.. Replaced the cartridge today. Before doing it I spent a while to check the chamber and it was completely empty.

And now the problem is entirely solved.. The taps trigger the boiler as soon as they are switched on.. And I checked the push rod into the microswitch and where as before it was "limp".. Its now shoots out like a dog on heat.

Thanks for your help

Jon