Cleaning plate heat exchanger issues

[0Floz0]

Hi all,

Going to be doing this shortly and I’ve read numerous threads but the info is contradictory and I’m going round in circles.

I’m seeing people say don’t use hydrochloric acid to clean the plate heat exchanger but then seeing people say to use spirit of salts. From what I gather, they’re the same thing. I’ve got a big bottle of brick acid which is also hcl acid so was thinking I could use this.

I’ve got a vaillant ecotec plus 831 and it looks as though the phex is stainless steel.

Another thing that seems to be contradictory is that some say only do the one side whereas some soak it in a bucket, so no doubt both sides will end up being done.

Any advice would be appreciated (other than buy a new one )

Cheers

 

[martygturner]

Personally I have used whatever came to hand, brick acid, spirt, but citric acid does they job and as its used in foods is pretty safe if your are a bit paniky about washing out the exchanger. You really need to just wash out the exchanger with a hose after you have finished.

You can buy Fernox DS40 but amazon do plain old citric https://www.amazon.co.uk/DriPak-Cit...g&qid=1745139897&sprefix=citric,aps,99&sr=8-8 or any big supermarket stocks it.

Mix with boiling water and fill up the exchanger.

 

[Johntheo5]

For interst.
I took a few readings and did a few calcs from someone with a WB 36CDI who installed a new PHEX as the boiler was shutting down on combustion chamber o/heat at ~ 85C I think.

What is surprising is the very big increase in the primary flowrate from 8.2LPM (fouled PHEX) to 23.0LPM (new PHEX) with practically the same DHW flowrates and mains temperature, see below.
Fouled PHEX. Primary: flowtemp/returntemp/dT/flowrate 71.5C/42.8C/28.7C/8.2LPM
(DHW) Secondary: Mainstemp/DHWtemp/dT/flowrate 19.0C/44.5C/25.5C/9.2LPM
Boiler Output 16.4kW
NEW PHEX. Primary: flowtemp/returntemp/dT/flowrate 64.5C/49.5C/15.0C/23.0LPM
(DHW) Secondary: Mainstemp/DHWtemp/dT/flowrate 19.6C/54.5C/34.9C/9.9LPM
Boiler Output 24.1kW

 

[gas112]

fill it Bick acid for 20 mins flush it all out then fill again for about ten mins then flush be as good as new.
Usually only need to do heating side

 

[0Floz0]

Personally I have used whatever came to hand, brick acid, spirt, but citric acid does they job and as its used in foods is pretty safe if your are a bit paniky about washing out the exchanger. You really need to just wash out the exchanger with a hose after you have finished.

You can buy Fernox DS40 but amazon do plain old citric https://www.amazon.co.uk/DriPak-Citric-Natural-Appliance-Descaler/dp/B076FCJLHL/ref=sr_1_8?crid=2GREP6MOB028X&dib=eyJ2IjoiMSJ9.kGriSoQObj5jYwz8l275XMFeL-aEentQOwoCwcnKQynmlH6LHzc_pKOh4vMMJFuHQUouOHNikDiH7DsiM6oezBw2cAWQUeRnPfJsHjFF0P3q76ZduO0w5Ea1VW-wb5HbaEmQVhdDPn3_Evtt18A8Tyk2lec5LTdHDSmiCSlTVoUnbc2RS8IU3lQk8HOMhP6wXlavo-MdKIW3peq97u81gjIivIrEIQcMzdOUZrP-fpfVecumKmiTLO5Gq_fggRj3AxcaOOln78dstXlYfZ6iWPIvshti_djZe5HlfSVxZqs.YQNRfOqVDNoqqm86RFVYRiUYkMUObZbVlK5Nns9mqw0&dib_tag=se&keywords=citric+acid+for+cleaning&qid=1745139897&sprefix=citric,aps,99&sr=8-8 or any big supermarket stocks it.

Mix with boiling water and fill up the exchanger.

Thanks! Might get a tub of Citric acid then. Any other things it’s useful for? Do you fill the whole exchanger or just the one side? Does it even matter as long as you thoroughly rinse it out both sides?

fill it Bick acid for 20 mins flush it all out then fill again for about ten mins then flush be as good as new.
Usually only need to do heating side

Cheers! Do you just fill the one side normally or drop it in a bucket of it and then rinse it out?

 

[0Floz0]

For interst.
I took a few readings and did a few calcs from someone with a WB 36CDI who installed a new PHEX as the boiler was shutting down on combustion chamber o/heat at ~ 85C I think.

What is surprising is the very big increase in the primary flowrate from 8.2LPM (fouled PHEX) to 23.0LPM (new PHEX) with practically the same DHW flowrates and mains temperature, see below.
Fouled PHEX. Primary: flowtemp/returntemp/dT/flowrate 71.5C/42.8C/28.7C/8.2LPM
(DHW) Secondary: Mainstemp/DHWtemp/dT/flowrate 19.0C/44.5C/25.5C/9.2LPM
Boiler Output 16.4kW
NEW PHEX. Primary: flowtemp/returntemp/dT/flowrate 64.5C/49.5C/15.0C/23.0LPM
(DHW) Secondary: Mainstemp/DHWtemp/dT/flowrate 19.6C/54.5C/34.9C/9.9LPM
Boiler Output 24.1kW

That’s quite the difference. I wonder if that’s a cause for my shower not having a great pressure on the hot water. Thanks for posting!

 

[martygturner]

Thanks! Might get a tub of Citric acid then. Any other things it’s useful for? Do you fill the whole exchanger or just the one side? Does it even matter as long as you thoroughly rinse it out both sides?


Cheers! Do you just fill the one side normally or drop it in a bucket of it and then rinse it out?

you need to hose out both sides so it doesn't matter

 

[gas112]

Cheers! Do you just fill the one side normally or drop it in a bucket of it and then rinse it out?

yep just the one side normally no need to drop it in a bucket

 

[Johntheo5]

yep just the one side normally no need to drop it in a bucket

Do you mean to just clean the secondary (DHW) side?, my post #3 above says that the primary side saw a huge increase in flowrate, which would say that its prudent to clean both the primary & secondary sides?

"from 8.2LPM (fouled PHEX) to 23.0LPM (new PHEX) with practically the same DHW flowrates and mains temperature"

 

[kidgreen61]

Normally only primary (heating) side gets clogged.
Brick acid is my go to solution.