Biasi riva advance overheating

[DanDIY]

Hi,

I have a biasi riva advance 32HE. Its about 3 years old.

The DHW temperature is cycling. The water is getting up to full temperature, then it cuts out and runs cold, sometimes the burners will reignite and it will continue to cycle from hot to cold.

Sometimes the thermal cut out will cut in and the boiler has to be reset. It also appears to be venting out of the overheating pipe that goes through the wall to the outside.

So far I have:

Checked the resistance of the DHW temp sensor. It seemed ok, but I replaced it anyway as it was only 4 quid.

Checked that the over temp sensor was reading closed circuit. It was.

So basically it seems that the boiler is getting too hot......or at least it thinks it is too hot.

The manual suggests that the fan could give issues with temperature stability. Does this sound reasonable, does anyone have any advice for checks on this - the manual doesn't say much?

Cheers, Dan

 

[Agile]

I presume you have the M110 model ?

The manual is produced for qualified and experienced boiler engineers and not foy DIY repairs by the boiler user!

A very quick search on this forum would immediately show that DHW goijng hot/cold is a typical symptom of a blocked secondary heat exchanger.

Usually results from a careless installer who did not boiler to power flush or otherwise properly clean the system!

Tony Glazier

 

[DanDIY]

Hi Tony,
Thanks for your helpful reply. I did try some searches, but after reading your reply I searched for blocked heat exchanger and my symptoms sound similar.

You are correct, there was no powerflush performed. The boiler was a new installation. There was a bottle of cleaner and inhibitor put into the system though.
If the heat exchanger is the issue the only thing I can think of is a weeping radiator bleed nipple in our bedroom, could this have caused gradual dilution of the system??? Although I'd be surprised if such a small leak, maybe a few cc's a month could lead to this?

My dad and brother are corgi/gas safe engineers, however as repairing modern boilers seems to be 80% electronics nowadays (and I understand that side best) I posted the question. I would not go breaking into the combustion/exhaust system, but consider myself perfectly competent to measure the resistance of a couple of thermocouples - regardless of what the law may say! I'll let them know that you consider them careless


I clean heat exchangers at work using citric acid to dissolve limescale. Is it feasible to get my tame corgi engineer to remove it so that I can clean it, or do you clean them on the boiler?

Cheers,
Dan

 

[Agile]

If the system was PROPERLY cleaned then it is unusual.

The usual fault is they use too much flux and the acid causes rust flakes from the inside of the rads. Very few properly flush and use the right chemicals.

Its easy to diagnose if you can accurately measure the temperature of the flow and return of the boiler on DHW. It should not be much more than about 15 C.

A very simple test is the tiny temp gauge on the boiler. On DHW it should not go much above about 65C at normal settings. I would expect its about 75C or higher?

They are best cleaned by taking them out and using citric acid.

To remove lime compounds you need sulphonic acid NOT citric acid.

Tony Glazier