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Back 105 HE Correct Valve Pins

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csreades

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I’m having issues with my central heating on a Baxi 105 HE. The HW works fine, the CH calls for water but the water doesn’t leave the system. I expect it’s just circulating around the HW loop.

My question though, is in proper operation what should the pin valves do. We have two that can be see. Front and Top.

The front is understood, it protrudes when there is a differential in the cold-hot water tap circuits, so open a tap, pin comes out, calls to heat.

However what does the top pin do? I don’t know for certain and my boiler isn’t working so I can’t tell if it’s operating correctly (expect not though).

So the top pin, is out = HW loop bypass enabled?

Or is it the opposite, and how does boiler pressure and pipes lead to the pin protruding, it isn’t as obvious as the front pin and I am looking to understand it as much as fix it.
 
So after I posted I was recommended a thread that told me what the other pin does. It signals that the pump is running, and should be out while the pump is on.

If that’s the case where does the CH/HW loop bypass occur or get controlled? Is there a way to know if it is mistakenly open?

So looking over the manual again, the HW pin I mentioned before, once out a tiny bit opens the bypass. My issue is that it is not closing enough. So likely the spring has gone and needs replacing. Pushing the pin in manually caused the radiators to heat up!
 
Last edited:
The pin rises with the pump running..it's part of the safety system ensuring sufficient water in the primary heat exchanger and the pump is circulating. Differential pressure (between the pump inlet and primary hex outlet) is applied to the diaphragm below the pin.

I'd first check the filter in the front section of the heating return isolating valve (behind the filling loop connection if it's an integral loop).

The bypass opens if there's excessive pressure between the flow & return eg. all the TRVs/wheelheads are closed down...it ensures a minimum flowrate through the heat exchanger and reduces the potential for TRVs to resonate with a high differential pressure across them.
With all the radiators open and a clean filter the bypass would normally be closed..ie. the pipe cool. They can jam open but it's rare.
 
the pin that comes out when HW demanded is on a plastic cone that gets brittle and breaks so after demand the spring cannot push it back into rest position that is CH which is why when you manually pushed it back you got CH . Pin might also be that cruded up its sticking instead of going back into rest position
you need this cheap service kit .
Change the two plastic bits with the pins on grease them and also change diaphragm and the gland nut on the front of housing that the pin comes out of
www.ebay.co.uk

Baxi Combi 80E 105E 105HE Diverter Valve Kit 248061 248062 NEXTDAY DELIVERY | eBay UK

BAXÄ° COMBÄ° 80E 105E 105HE DÄ°VERTER VALVE REPAÄ°R KÄ°T 248061 248062 NEW - 24 PART. BAXI COMBI 105 HE (SHORT PARTS LIST). BAXI COMBI 105 HE (HYDRAULICS). BAXI COMBI 105e (SHORT PARTS LIST). BAXI COMBI 105e (HYDRAULICS).
www.ebay.co.uk
 
Thanks for all the information, bought that kit and will fit that! Hoping it’s as simple as that as I hate having to go further back on the diverted valve. These things don’t seem built for easy servicing! (Likely not helped by its location in the room!)
 
Popping this to the top. I followed suggestions and changed those components. It seemed to help but actually only one tap in the house was able to make the pin come out enough to press the switch and start the heating. However the plus side it did go in enough to start the heating.

For now I have put in a weaker spring I found in my bits box that fit. This weaker spring means the CH bypass wont close, but at least all the taps call for hot water.

Any thoughts, it seems like there might be a blockage somewhere so that only one tap can provide the pressure difference to push the diaphragm [ I tried the old and new diaphragm and both behaved the same].
 
Yep venturis fall apart and can stop the diaphragm moving enough 24mm ring spanner required for changing them
Then check in hole for any of the broken bits if there is tape a bit of garden hose to hoover hose and suck them out .

.
the venturi is on the lefthand side of the righthand brass section just below where the 2 small pipes from diaphragm housing connect
 
Appreciate the comments, I will have a look at the Venturi tonight. Unfortunately the kit I got didn’t include and service parts for it so hopefully I can clean it and have it working tonight!

I sometimes wonder if it might be time to get a new boiler…
 
Fairly sure that will be the problem... took that part out and the case has disintegrated and the spring was just loose! Unfortunately I don't think any local shops sell the part so amazon it is!
 
Sorted! I have hot and cold water. For anyone else in the same boat the link above to the part is correct, but there is a sub-assembly (which I needed replacing). It cost more than those online, but I was able to get it from a shop same day:

Baxi hydraulic venturi assembly | Wolseley

Looking for a Baxi Venturi Assembly 248051? Order from Wolseley today - free delivery or click and collect available nationwide.
www.wolseley.co.uk www.wolseley.co.uk
 
csreades said:
Sorted! I have hot and cold water. For anyone else in the same boat the link above to the part is correct, but there is a sub-assembly (which I needed replacing). It cost more than those online, but I was able to get it from a shop same day:

Baxi hydraulic venturi assembly | Wolseley

Looking for a Baxi Venturi Assembly 248051? Order from Wolseley today - free delivery or click and collect available nationwide.
www.wolseley.co.uk www.wolseley.co.uk
Click to expand...
You’re welcome
 

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