Siemens DVA3 (3-port valve) body only replacement

[iwbnwif]

Of course it couldn't have happened in the summer...

No hot water, traced to no hot going into the cylinder heat exchanger.

I suspected that it is being caused a faulty / seized 3-port valve so popped the actuator off and tried to move the spindle by hand which it didn't.

So I tried again with a pair of pliers which was a mistake as even though I wasn't particularly rough, the spindle simply split and the top came off.

The actuator seems to still be working fine (selecting hot water on/off causes it to move approximately 30 degrees).

I have found a replacement body online https://www.heatingcontrolsonline.co.uk/siemens-22mm-3-port-valve-body-only-p-336.html.

Is it necessary to remove the whole valve, or can I just take the 4 bolts on the top out and replace the spindle? Is it necessary to drain the system down?

 

[Hugh Jaleak]

You'll need to drain down, I'd be inclined to replaced the whole thing, splitting it could cause it to leak. Don't forget to top up the inhibitor once refilled and tested.

 

[iwbnwif]

Thanks for the fast response.

I've got a bottle of X100 ready and will probably take the opportunity to flush the system a couple of times first. I've also got a bottle of X200 that I have been meaning to try for some time - so may give that a go as well. It was going to be a job for the Spring!

 

[Hugh Jaleak]

If you think the system is a bit mucky, I'd look to drain the lot down, (you've got to get below the level of that valve anyway), and chuck a bottle of X400 in for a few weeks. Let it do its job, drain and flush several times then refill adding your X100 and the X200 if needed.

 

[iwbnwif]

Thanks, that's a good idea .

I did flush it about 4 years ago with X400, but given the age of the system (about 30 years) it is probably due again. Also, probably worth doing when it is running more or less 24 hours a day as it is at the moment.

 

[Hugh Jaleak]

If you've maintained the correct level of inhibitor in the system, it shouldn't need flushing at all in my opinion. A lot of the build up of crud is due to the electrolytic reaction between the different metals used in the system, the inhibitor, does what it says on the tin, and inhibits this.

Powerflushing is often required prior to fitment of a new boiler, but that is the Boiler manufacturers method of ensuring the boiler isn't fitted toi a dirty system, which in turn could clog up/wreck the boiler.

Depends what colour the water comes out, fairly clean and I wouldn't worry, if its black then you need to clean it out and treat system accordingly.

 

[iwbnwif]

Sorry, flush is the wrong word. What I meant was drain / refill a couple of times, then add X400 for 2 weeks, then drain / refill a couple more times before adding a bottle of X100.

Since then it has been untouched, but it should be okay. Like you say, I will see how it looks before deciding.

 

[Hugh Jaleak]

That's what I'd class as a chemical flush, often more than adequate if system isn't too badly sludged, and you just wish to improve performance.