Oscilating water temperature, black flakes in theheating system

[iwantashower]

Please excuse the lack of technical terminology - I'm just a wife frustrated with the never-ending heating system dramas and a husband who is even more frustrated with it ...

So here's the problem: it all started when one day our baxi boiler started oscillating ... a lot! So we called a gas engineer who had a quick look and sorted it in minuted by installing a new heat exchanger, informing me that the old one was blocked ... Fair enough! It worked and we had lovely hot showers until ... a week later it started osculating again ...
So out came the heat exchanger cleaned out and put back in ... So another week and the invigorating contrast showers were once again a daily reality ...
This time the the heating system got flushed out, filter installed on the system, new heat exchanger put in again ... Hooray, we thought, it's over! But almost a week later the oscillation was back ...
Ok ... some of the pipework in the loft got replaced, ANOTHER filter went in, more flushing, more cleaning out ... And ... yes, you've guessed it - it all lasted about a week ...
The last attempt: new heat exchanger, new expansion vessel in the boiler, ALL of the heating system got flushed inc valves in the boiler, the piping manifold, each individual radiator take off and flushed ... EVERYTHING that we could think of was cleaned ... inhibitor in the system ... (lots of) ... And now ... TWO weeks after dreaded problem is back again ...

A few notes on the system: underfloor heating - pp piping, one manifold, acova column radiators on some walls - another circuit with own manifold, baxi combi boiler ... Installed three years ago. Worked perfectly with just the UFH, problems began after the radiators have been added. When flushing the system - clear water with black hard flakes and sand-like granules come out. I understand that the blocked h/exchager is what makes for oscillating water temperature. What I (and the engineer husband) fail to understand is where the residue is coming from ... Flushed several times, inhibitor added, everything seems to be in order ... I tend to look at the radiators with a sense of suspicion ... Internal damage? Perhaps some sort of anti-corrosion coating inside the radiator damaged? Manufacturing fault? Rust? If its rust - why black without a hint of brown? ...

Help! I NEED a sane husband back and a hot shower!

(all gas units have remained untouched and are intack - could there be a problem lurking there, if so - what shall I suggest the gas engineer to look at?)

 

[Ermintrude]

With underfloor heating it is essential that a biocide AF 10 or similar is used. Who fitted the rads and were they clean? Sounds possibly like foundry sand from rads were made. Do u have any of the rad sand. ? "Claim" !!!! It won't only be the plate exchanger but the main burner hex that's going to be a mess. Get some of the sand, get your receipts for repairs and the boiler and go see the supplier! Your going to need a powerflush. Also I would never recommend a tf1 as I'm a Magnaclean man, but the tf1 will collect the sand. Or you could get a Magna clean two tec (more expensive). Filter is to collect any sand left in.

 

[erpkid]

Have you got a water softener? If so and it is a little long in the tooth the membrane can collapse releasing the contents which could cause problems with your heat exchanger. I think Ermintrude has covered the other angles. Welcome to the forum.

 

[chris watkins]

If you believe it is coming from the rads why not turn them all off & just run on the U/F while it is still fairly warm, if it lasts longer than a couple of weeks you will know.

 

[Dotty]

If necessary ask your gsr to install a y strainer on the return.



CHECK & RELIEF VALVES, STRAINERS & DRAIN COCKS

 

[Ermintrude]

Won't it block up and cause boiler to overheat ?

 

[Dotty]

Possibly, but what's more of a pain in the bum? cleaning out a strainer or a heat exchanger?

Bang a valve either side and make it a weekly cleaning schedule until it runs clear.

Or install one of the traps the capture magnetic and non magnetis detritus - Can't remember which one does that though... Trappex?

 

[Irish]

I fitted 4 of those avoca column rads (customer got them from b&q) last year and I couldn't believe how much swarf was in them spent 10 minutes on each tryna clean it out of them I'd never use them again

 

[iwantashower]

Thank you! We did worry about the possibility of more damage elsewhere where we can't get to ... Oh well, get the receipts together, I guess ... Powerflush booked ...

 

[iwantashower]

Thank you for the replies!
No, no water softener.

Isolated the rads after the last time we flushed the system, were really happy when after a week it was still working but then ... back to square one ... hence the post here ...

Will be powerflushing next week ...

Thanks again, everyone!