Baxi proving pin

[Eamonn Cooney]

Hi Darren, sorry to jump on your thread but I have nearly exactly the same problem with exactly the same boiler.

I have so far cleaned out the flow valve, replaced the diaphragm, cleaned the pin and put new silicone Plumba grease on it.
I've also checked the heat exchanger for blockages (was replaced only last year and very clean).
I have an external pressure vessel and the main line to it was clogged. Cleaned that out and flushed it, checked charge in pressure vessel at 2 bar (also replaced last year).

Recharge system to 1-1.5 bar and the proving pin FIRES into life. After running the boiler for a few mins the pin gets weaker and weaker.
Boiler kicks off and on reset the pin does not push out any more (or just a little). Bleed all radiators but still no major movement on the pin.
I've got a mag filter on the return line and have checked that (all clear bar a little bit of buildup).
Reconnected, bled, still nothing.

If I restrict the flow on a main valve the pin comes out.

I'm thinking either a fault flow valve (even though I have checked it over) or a blockage somewhere else in the circuit.

Any ideas would be greatly appreciated.

 

[ianmcd]

It is against site rules to Hi-Jack a post for very good reason, if you want the correct advise you have to start your own and dont cross referance this post as you dont have the same boiler

I've also checked the heat exchanger for blockages (was replaced only last year and very clean).

you have a combi not a system boiler

 

[DarrenNewsgroup]

I can't comment on what your fault is as I am just a home user who is willing to take on simple DIY jobs with guidance from experts.

My own personal guess with your problem is that the pin is fine but it gets weaker because the water flow is getting weaker (so the pressure holding the pin out gets less and less until it can't hold the pin out any longer). I think the pin and the diaphragm is fine. Is it a failing pump or water pressure sensor failure? Just my 2p worth. Hopefully the experts will chime in with the real cause.

I had put a 6 month reminder in my calendar to report back on my "boiler repair" so I will do it now...

After cleaning the pin, as described by the experts here, I have had absolutely no more issues with the pin sticking. My boiler is working perfectly again.

Thanks everyone for your help.
Darren

 

[Eamonn Cooney]

It is against site rules to Hi-Jack a post for very good reason, if you want the correct advise you have to start your own and dont cross referance this post as you dont have the same boiler




you have a combi not a system boiler

Hi Ian, sorry for breaching rules. I don't have a combi boiler. Mine is the same as Darrens.

 

[ianmcd]

Hi Ian, sorry for breaching rules. I don't have a combi boiler. Mine is the same as Darrens.

so the heat exchanger you changed was the main heat exchanger ? never had to change one ever, have you checked the pump ?

 

[Eamonn Cooney]

so the heat exchanger you changed was the main heat exchanger ?

Yes correct, it was changed last year.

 

[ianmcd]

have you checked the pump? when you changed the diaphragm did you clean out the small orifice under the diphragm /

 

[Eamonn Cooney]

Hi Ian, yes pump is perfect. I swapped it with an old pump (know to be working) I had just to test and both were running the same.
I took the entire hydraulic assembly out and gave it a good "once over" cleaning everything but to be honest it was spotless inside apart from a small amount of buildup on the front cover.

 

[Gasguru]

How did you test the pump?

 

[Eamonn Cooney]

How did you test the pump?

I removed the pump, checked to make sure the impellor was intact with no broken fins etc. shaft is not seized as it's working perfectly with no vibrations or noise.
I swapped it just in case it was down on power for some reason but the other pump was exactly the same.

Am I doing something wrong to test the pump? Is there a better way?

 

[Gasguru]

The impeller might be clean and free but there's more to it.
Make sure the earthing to the pump is fully intact.
With a leather glove or cloth on the impeller power up the pump and try to stop the impeller from turning.
A new pump should put up a fight...as they age the impeller is easily stopped or prevented from turning at switch on.
It's down to experience but you get the idea.

 

[Eamonn Cooney]

I have a theory

The impeller might be clean and free but there's more to it.
Make sure the earthing to the pump is fully intact.
With a leather glove or cloth on the impeller power up the pump and try to stop the impeller from turning.
A new pump should put up a fight...as they age the impeller is easily stopped or prevented from turning at switch on.
It's down to experience but you get the idea.

Great, thanks for the advice. Will give that a go later. I'm nursing this boiler until a new replacement is installed.
We are currently in the process of completing an extension where the old circuit will be incorporated into a new one but for now it's untouched.
It's been acting up for a while now but hopefully I can give enough CPR until it's time to replace.

 

[Gasguru]

With the older pumps you can access the end of the pump shaft through the bleed screw...a 4mm flat head will fit the Grundfos so you can sometimes test the torque from there.