Viessmann F2 Boiler Fault

[cr0ft]

Hi all,

Been contacted a month or so ago by a customer who wanted their system powerflushed on the advice of a Viessmann engineer. The customer has a Vitodens-100W 35KW Combi boiler in their house. The Viessmann engineer removed and cleaned the secondary plate heat exchanger in the boiler and pulled some fairly sizeable (up to 5mm across) flakes of magnetite out of it.

We have been to powerflush the system. Here's where it gets odd! We connected the powerflushing machine up on the return pipework below the boiler (split the pipework and connected onto there). The whole system was then properly powerflushed. The boiler worked fine for about a week then the issue returned. Previously the F2 fault (circulation issue) only occurred with hot water being called for. Now the boiler is starting to cycle on central heating mode too. On looking at the boiler it is very quickly going from 30 or so degrees up to 90-100 degrees. This rise only takes a minute or so. It then cools and repeats. Because of this the furthest rads on the system are now not getting warm.

Did a customer service visit tonight. Our engineer has certainly got the system clean and I've seen no sign of any airlocks. We took samples from a couple of radiators and also from under the boiler, the water is nice and clear. Despite this, something is stopping circulation. My initial thoughts were that the primary heat exchanger might be clogged up but this isn't possible as the powerflusher would always be sending water around the primary heat exchanger. I think it's not possible this could still be blocked.

Which leaves the pump inside the boiler as the only possible problem, right? or wrong? Would appreciate any thoughts, particularly from anyone who has experience with Viessmann combis!

 

[jonnyswamp]

Not a lot of exp with Viessman's, but can you remove and strip/inspect the pump easy enough
Veins could be clogged

 

[ShaunCorbs]

whip the pump out will tell you if any doubt phone tech up there a great set of lads pm me if you want the no

 

[townfanjon]

I have had the plates out blocked with crap before, that could quite easily be blocked up, but this wouldn't explain probs with the heating. I use a magnacleanse , personally I wouldn't put a power flusher through a boiler, and tbh don't know if you should .

 

[cr0ft]

Hi all. Thanks for the replies. I'm not convinced the powerflush has made it worse to be honest. I think there was a gradually worsening problem in there that started with the hot water. It did get better after the flush for around a week and I'm very happy there is no crap left in the system (outside of the boiler at least). Pretty sure the main heat exchanger will be clean now too.

To be clear, we powerflush with a powerflushing unit and a Magnacleanse in series so it's picking up all the crap from the system very quickly.

Pump definitely sounds plausible, am going to recommend popping back to check the pump. Is it possible to check a pump is working properly based on the current it is pulling? I've heard that some boilers can have the pump start to slow down as it gets older. This would be harder to identify right?

I have to assume that the secondary heat exchanger is reasonably clean now as it was washed out by a Viessmann engineer last week. As folk have said it wouldn't explain the issue on heating that's started over the last couple of weeks.

 

[hammers4spanner]

Ping back to veissman if its under warranty or go on Facebook where veissmans are worshipped