Biasi 24S dhw fault

[speshfesh]

Hi Guys,

I seem to have quite a common fault if the number of posts are anything to go by.
Firstly let me state that I consider myself to be a competent DIYer and I am an electrician by trade so I'm not averse to a bit of tinkering but I know my limitations.

And so the fault...

1. No dhw (cold from tap)
2. Changed diaphragm in the hydraulic actuator (no joy)
3. Changed O-rings on the 2 x micro pipes from actuator housing to main inlet housing (mains water inlet) because I had a slight leak after changing the diaphragm
4. ch works fine and to correct temp
5. Main flow switch operates correctly
6. Diverter valve not operating to push dhw flow switch (hence my thoughts on changing diaphragm in 1st place)
7. If I manually operate the dhw flow switch, the fan, pump, etc operate ok (but no ignition due to no detectable flow I guess?)
8. If I disconnect the hydraulic actuator housing and move it to one side (leaving small bore pipes connected) and manually push the pin (manually doing what the actuator is supposed to do) the dhw operates perfectly and to temp.
9. Checked flow switch voltage at pcb (13.75vd.c.(ch) and 0v (dhw))

I have still got a slight leak from one of the micro bore connecting pipes from the hydraulic actuator. I need to know if this will result in a drop in usable pressure thus not delivering the pressure needed to allow the actuator to move the diverter valve mechanism.

I should add that:
1. I have stripped the DV and cleaned everything up.
2. When I had the actuator housing to one side, I opened a hot tap and the actuator moved to it's full position hence my question on pressure above.

Jeez sorry for the essay, I've got 4 kids all screaming for a bath (Gran's at the end of her tether methinks!).

Appreciate any insight on what to do next.

 

[Agile]

Take off the diaphragm unit and momentarily pressurise the system and see if water comes out of BOTH tubes.

Its possible that one of them has become blocked.

If water comes out of both then you need a CORGI to remove the gas valve and a 24 mm spanner to remove the filter/flow restrictor in the right hand hydraulic block. Its just possible the plastic cage has fallen apart and is not delivering the differential pressure.

Be aware those situations are rare but you do seem to have clearly explained the situation and that only leaves one of those two possibilities.

Your line 7 is not consistent though, assuming you remembered to have the system pressurised ???

Tony Glazier

 

[speshfesh]

Thank you Tony, I was hoping you might be the one to answer!

Sorry about line 7, yes the system was pressurised when I manually operated the DV mechanism.

1. Filter/flow restrictor - right side of DV?
2. Can I avoid removing the gas valve and remove the DV instead? (I understand removing the gas valve wopuld probably be a quicker job).

Take off the diaphragm unit and momentarily pressurise the system and see if water comes out of BOTH tubes.

Do you mean remove the 2 pipes from the diaphragm unit? Sorry should have mentioned I removed pipes and checked for blockages (both clear) will do what you've asked regardless.

Thanks again for the reply.

 

[Agile]

1. Filter/flow restrictor - right side of DV?


Thanks again for the reply.

NO, as I said its on the lower left side of the RIGHT hand hydraulic block.

It cannot be removed without taking out the gas valve!!!

I suppose that with a lot more work the RH hydraulic block can be taken out of the boiler leaving the gas valve in place.

But then I would not know because I would always remove the gas valve!

Tony

 

[speshfesh]

Sorry Tony, just took a look at the manual, I get where you're talking about now. I should be able to pick up the dhw filter and pressure reducing valve kit without any trouble.
Thanks again for the advice, always best to ask the experts.

 

[ChrisR]

Your line 7 is a problem. If you manually operate the switch, the boiler only thinks hot water's flowing, it doesn't know anything else. The diverter is in the wrong position, but it doesn't know that (CH). So the boiler should have lit.
You said the pump ran - that should operate the flow switch regardless.
I though the flow switch had to operate on that boiler BEFORE the fan would come on.
SO try it again!!

I'll just have a look at the manual...!

 

[speshfesh]

Thanks for the reply Chris, to be honest I may be getting a little confused (hours sat trying different things and trying to look at things logically!). I'm certain the pump was running but I could have been mistaken.
Sorry I know this is frustrating for you guys 'in the know' (I'd be the same with electrical stuff!).

 

[ChrisR]

This is about what you should find on the right...

 

[speshfesh]

Thanks for all your help guys, much appreciated.

 

[Agile]

If the right hand part with a plastic cage and spring and plunger has come apart then it will not produce enough differential pressure to operate the diaphragm.

I must stress thats very rare but you have been good at describing what yuo have done and if the tubes are free and the diaphragm is correctly assembled and the mushroom part moving freely then its all thats left !

If those parts are broken/missing then they will be somewhere and you should look at the CW inlet to the plate HE to hopefully find them. They might also be lodged inside the RH block too.

Tony

 

[speshfesh]

Thanks Tony,

I had a feeling I was getting to the point of narrowing it down, I just didn't know where to look next.

Thanks again to you and Chris. I'll post if I'm successful.

 

[speshfesh]

Yep, venturi and flow regulator totally wiped out. Retieved what I think is all of it (total mess). Got new entire assembly coming from Ezypart.co.uk (reasonable price too I think @ £23.57 next day to the door).

Don't you just love a happy ending? (just hope it's in stock now )

 

[Agile]

Nice to know I got it right!

Thats a very unusual problem though! I might see one every THREE years!

Its lucky that you clearly explained what you had done because that encouraged me to help you with this unusual fault!

I would have sent you one for £20 !

Tony

 

[speshfesh]

£20? Dammit!! I hadn't realised and I could've given you some business for your trouble! Oh well, I'll know if there's a next time.

I would add that, I have a slight leak from the right side of the DV (dhw flow sw side). Can I PTFE or Hawk White the plug? Or is it due to the increased flow? (due to no flow regulator at the moment). I've tightened it as much as I dare.

I'm off to Buckinghamshire for a meeting today so I'll check back this evening (wouldn't want a slow reply to appear ignorant).

 

[Agile]

The gland on the flow switch is a fabricated unit and contains a rubber "O" ring.

It needs to be replaced ( about £8 ) but its essential that the pin shaft is completely cleaned and lubricated with silicone grease otherwise the new gland will fail prematurely.

If they have been leaking very much the switch may have been damaged!

This normally needs the gas valve to be removed to gain access although I have changed one without but its very tedious.

The non-CORGI way is to remove the entire LH hydraulic block!

Tony