BIASI boiler runs hot then cold - help!?

[johncross85]

Hello!

We have a BIASI M90E 23S which seems to be playing up a bit...

My wife complained that the water was going from hot (normal temp) to cold. I looked at the water pressure on the boiler and it had dropped low. I topped it up to 1 bar but later that day when the central heating ran the boiler spat out water from underneath. I ran the central heating and found that the water pressure quickly rose from 1 bar to 3.

After doing some googling I found this site and swiftly came the conclusion that the Pressure Vessel needed repressuring. I followed the instructions from the (rather excellent) FAQs and I think successfully repressured the PV to just under 1 bar.

When I now run the central heating the water pressure goes no higher than 1.5 bar and all seems well. I had hoped that this had fixed everything but it turns out the hot water still runs hot and cold!

I ran the hot water while listening to the boiler and the boiler appears to run okay for about a minute then clicks off for maybe 10 secs, then comes back on for another minute etc.

Could this be a symptom of my PV repressuring not being 100% successful or is it likely to be a separate issue? If so, any ideas what?

Thanks for any help!

John

 

[lightning]

Blocked plate exchanger

 

[johncross85]

Blocked plate exchanger

Okay, thanks. So is it a case of just flushing it out or replacing it altogether? I ask because our usual plumber has gone awol of late so I'd like to have a heads up as to what to expect before getting someone new in.

[Edit] Forgot to mention - The boiler has been running fine since we bought the house 3 years ago. Is it likely that the blockage has suddenly occurred or would it have built up over time?

Thanks!

John

 

[Agile]

The plate HE can be cleaned but thats messy and not all engineers will do it. Some just shake out the dirt but thats not very effective at removing all of it.

I seem to be one of the few who will clean them. Even so it takes quite a while and needs the appropriate chemicals to be used. With common boilers I just take along a ready cleaned replacement to save time on site.

Many will just replace the plate HE but thats a more expensive solution.

Although its most likely to be the plate, there can be other causes as well.

Please note that your boiler is an M90 28S. It has a different ( larger ) plate than the M90 24S.

Tony

 

[johncross85]

Thanks for the help Tony! I've just had a look on the United Utilities website and it looks like we're in a hard water area so chances are that the culprit is limescale built up over time. Time to hand the problem over to a plumber...

Thanks again,

John

 

[Agile]

Its most likely to be dirt in the system.

Even in very hard water areas, lime scale is very rarely going to cause any problem with the plate HE unless you have a dripping tap or the boiler has a fault.

Tony