Back 80HE stuck pressure differential assembly?

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Jon2412

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hi all,

I have a Baxi 80He boiler. Rads we're working fine but no Hot water.

Have checked that the flow sensors were working, pump was clearly working, system pressure correct, boiler firing as expected and temp sensors indicating rise in water temp on the front display.

I noticed in hot water mode that the boiler feed and return pipes were baking hot. The motorised actuator on the diverted valve is operating and the water flows through the how water pipes around the boiler. (I checked by touching and checking the in/out flow pipes going to the expansion vessel at the back of the boiler) However the heat exchange plates remained cold whilst bypass pipe got very hot. Rads are not heating up when hot water is demanded so this all indicates to me that the main diverter valve is operating as expected.

I have taken off the plate heat exchange and it's not clogged. I have removed the front diaphragm on the pressure differential value unit and it is working and freely moving however I have now seen that the pin in the main body of the differential valve assembly appears to be stuck in?

Having done all the other checks this would appear to confirm that water was only being diverted into bypass and back round the boiler.

Is the assembly something that can be refurbished or should I be buying a new unit? It's a real pain to get out as I can't quite get in to undo the bypass pipe feed, so before I take it any further and buy a fairly expensive unit I wanted to check if anyone had other thoughts!

Thanks for any advice/thoughts!
 
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I normally replace the whole assembly for a customer.

But it is possible to take it apart and clean it and reassemble.

Once I did that for a customer friend and spent a while even boiling the bits in citric acid. But it still jammed again a few weeks later. So never again.
 
Thanks Agile. Does sound like it might be false economy to try and clean it up. I don't relish the idea of going through all this again in some weeks time! Between my time and replacement gaskets and things I think I shall pay up for a new assembly.

Though how on earth am I supposed to get the nut undone for the bypass pipe feed?! I've got the HW HeatEx and Pump out and I'm still struggling to get onto the nut and get some leverage (without bending the bypass pipe). It's not the easiest of access points!

Thanks
 
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Bernard has never repaired any boilers of course.

Particularly not the Ideal Isar heat only boiler,
 
Sounds like your talking about the INSTANT version of that boiler, and its the pin in the preheat diverter thats stuck (common fault).

You need a sturdy tap spanner (see link below for the one I use) with a wrench on the end to get the back nut undone, but in all honesty if the pin is showing no signs of leakage then you might as well remove just the front nut, clean/polish the pin and regrease. Take care not to distort that front nut when you undo it, as the P'Diff has got to fit back into it.

https://www.cromwell.co.uk/shop/han...nch-adjustable-basin-nut-wrench/p/MON5880345V
 
Flyingfish - thanks. It is indeed an instant version, my bad for not noting this up front.

Thanks for the advice on the tools - looks like I might need to buy one!

The front part of the assembly doesn't look like it is a screw fitting? The p/diff just sits on it with a clip and I see no obvious threaded section that would unscrew. Certainly it would make life easier if it did. Am I missing something, it looks like it's a solid unit (and no there's no sign of water leak so guessing gunked up internally)

Thanks
 
It does unscrew, and if it's dry, then go for it. It will be fairly tight, you just need to grip it without squeezing it. The force required can distort the round shape of your not careful. Depending on the tool you use. Normally a stubby wrench can do the job. Pliers can crush tho.
 
Jon2412 said:
Flyingfish - thanks. It is indeed an instant version, my bad for not noting this up front.

Thanks for the advice on the tools - looks like I might need to buy one!

The front part of the assembly doesn't look like it is a screw fitting? The p/diff just sits on it with a clip and I see no obvious threaded section that would unscrew. Certainly it would make life easier if it did. Am I missing something, it looks like it's a solid unit (and no there's no sign of water leak so guessing gunked up internally)

Thanks
Click to expand...
The castellated nut that takes the clip will screw off
You will get wet if pressure is not zero
Almost certain that part will be seized
Last one I cleaned and lubed. Unless leaking, have never had to replace the whole manifold
We like to call ourselves engineers , but then revert to part changing, not very engineering in my book
 
Ah okay thanks for this, that will make life a little easier perhaps. System is drained so no pressure in it and the inside of the nut is bone dry with no sign of leakage. Thanks for your replies. Most insightful.
 
Which are you trying to remove?

The one on the left with the motor actuator?

Or the one to the right with the diaphragm assembly?

Or both?
 
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