Combi boiler - bang when hot water opened

[andrew77]

Just noticed that its your boiler water pressure gauge thats jumping? re post 34 above, you need a tyre pressure gauge to stick on the air end schrader valve on the expansion vessel, you can then reduce the pressure to 2 bar by pressing the pin on the schrader valve to release some air until pressure gauge reads 2/2.2 bar.

Yes, it is. The other member has the same problem.

Thanks for explaining it. So, it all looks like I have everything installed what it's needed. It's just some balancing that needs to be done now on that mini expansion vessel. I can easily do this myself. I will post a reply with update.

 

[John.g]

No guarantees that it will cure the problem but worth a try anyway.

 

[ShaunCorbs]

4 bar seems very high how did you get this info ?

 

[andrew77]

4 bar seems very high how did you get this info ?

It says Precharge: 4.0bar hence my thinking.

 

[andrew77]

Ok, so I adjusted the pressure in that mini expansion vessel (2.0bar at the Pressure Reducing Valve and 1.8bar at the mini expansion vessel). It did help a bit as the bang it's slightly less louder, however it did not fully cure it. I think at this point I will probably get Viessmann to investigate or I might wait for the annual service and then have them investigate it.

 

[woytaz]

Ok, sorry, but I was bit busy in my life recently and I have forgotten a bit about this thread. So, I finally contacted Viessman, engineer just came and replaced diverter valve. It's just still fresh but so far so good. No banging noise after opening hot water when CH running. We will see if it's gonna stay like this, but surely it was a diverter valve problem. The engineer said that for some reason this valve was closing/openning too quickly where it should do it slowly. So @andrew77 , you need to push them to replace diverter valve, tell them about my case which is similar.

 

[andrew77]

Ok, sorry, but I was bit busy in my life recently and I have forgotten a bit about this thread. So, I finally contacted Viessman, engineer just came and replaced diverter valve. It's just still fresh but so far so good. No banging noise after opening hot water when CH running. We will see if it's gonna stay like this, but surely it was a diverter valve problem. The engineer said that for some reason this valve was closing/openning too quickly where it should do it slowly. So @andrew77 , you need to push them to replace diverter valve, tell them about my case which is similar.

@woytaz thanks for the update. It's funny because the very first Viessmann engineer (I had 2 different engineers from Viessmann checking this) that came actually mentioned that in his report he would mention that the diverter valve motor should be replaced. On the second visit another engineer came and he only replaced the gauge and did nothing to the diverter valve or the diverter valve motor itself. I am guessing that you probably had the whole set replaced.

I will be contacting Viessmann and asking them to do exactly the same to my boiler. I will 100% mention that this is not an isolated case.