Drain off for Microgenus

[AlexCarp]

Relatives combi has a blocked plate heat exchanger on a Microgenus 28MFFI, non condensing model about 10 years old. I diagnosed this by searching in this forum. Does anyone know where the drain off is on this boiler? Obviously I do not want to drain the whole system down if I can avoid it. On the CH return to the boiler the integral isolating valve has a big cap under it, while the flow isolator valve does not. Is this isolator and nut the drain for the boilers heat exchangers? If so how does it work?

 

[GodKnows]

Hi all,

I suggest you get a heating engineer to do the job, if you can't find the drain-off point on the boiler, then, you don't know what else is involved in doing the plate Hex replacement. You could cause more damage and money for your relative, if you get water on the PCB

 

[AlexCarp]

Hi all,

I suggest you get a heating engineer to do the job, if you can't find the drain-off point on the boiler, then, you don't know what else is involved in doing the plate Hex replacement. You could cause more damage and money for your relative, if you get water on the PCB

Believe me I am quite able to unscrew two hex bolts and pull out a plate heat exchanger. It's a combi not Apollo 13. I assume you do not know if this large cap is the drain then.

 

[Dan Robinson]

GK makes a very valid point.

 

[AlexCarp]

GK makes a very valid point.

Not in my case he doesn't. Do you know if this cap is a drain?

 

[Dan Robinson]

It's one of those questions.... if you have you ask....

Your research lead you to a couple of easy Gex bolts. Yet you haven't worked out the easy bit of draining the system/boiler?

Next you'll be telling us you fix fridges for a living.

 

[DP]

Go for it lad, undo the hex bolts. That will depressurise the boiler.

 

[mogget]

 

[AlexCarp]

Go for it lad, undo the hex bolts. That will depressurise the boiler.

It clearly will. I did another search on this forum and the cap is a drain off point. Thank you all for nothing and now you all know something

 

[Dan Robinson]

Wow. Not even 10am and a diyer has taught me how to drain a poxy microgenus. What will I fill the day with now?

 

[AlexCarp]

You have a vacant unfulfilled day ahead.

 

[Dan Robinson]

You wouldn't say that if you saw the lovely lady I'm driving to now.

 

[AlexCarp]

You wouldn't say that if you saw the lovely lady I'm driving to now.

One of those jobs eh !!!

Back to the Microgenus. Easy enough job to do despite the strange warnings on here. I Powered off the combi and opened the drain off cap and emptied the boiler and part of rads into a bucket and also opened the auto air vent on the top of the pump. I opened the rad vents part way through draining to avoid drips on the floor. Turned off the cold water to the combi and drained the hot taps. Put an old towel under the combi at the back. Took out the diverter valve motor head by unplugging the cable and taking out the spring clip. Took away the gas valve LED assembly from its holder which slides out. This gives space. The left hand hex bolt is easy to get off. The right hand one takes time turning the bolt 1/4 turn at a time and takes about 10 to 15 mins to take off. The pump can be removed to gain access, but patience can avoid that. There is enough space to take away the plate heat exchanger. A little water came out of the plate, only drips. None went on electrics as I had an old T shirt ready to wrap it in.

I blew through the plate. The primary side had a restriction compared to the DHW side, but not so much I though would make a difference. I banged the plate with the rubber end of a hammer lightly while flushing under the tap. Lots of back stuff came out in small flakes or just like large dust particles. I then soaked the plate in Silit Bang for 3/4 hour. Again I flushed it though and lots more black stuff and a little scale came out. I then mixed a heavy solution of soda crystals and poured that into the plate and left it for about 2 hours while I went shopping. Again I flushed out and hit with the rubber and lots more back stuff came out. It found this took about 20 mins before it was all clear. Blowing in the plate holes I found no restrictions.

I replaced all in the reverse order of taking them out. No leaks. The DHW all worked well and was even slightly hotter. This was to get them DHW ASAP. I have told them it needs cleaning out properly otherwise it will happen again and maybe soon. I told them a filter is needed on the CH return, which is easy to do, and X-900 put in and after the gunge is removed by the filter and the water runs clean, X-100 in to protect the system so it does not occur again. That is the next job within a week or two. The filter is good for the next combi if and when one is fitted and protects the rads as well.

The boiler's plate had a date of Feb 2003. So this is about ten years old and the first problem ever with the boiler. Not bad for a supposed crap unreliable make. If the filter was on when fitted (where they about then?) then this problem would not have arisen. I think the odd service guy did not replace the X-100 in the system. Although the stickers on the front of the boiler indicate so. Did he just put the stickers on? Or is inhibitor not that effective?