Inhibitor Renewal

[JSM]

Hi Wizards,

The plumber put inhibitor in my system when my house was built. Unfortunately, he doesn't know what type he put in so there is no question of topping up. How many years should I go before I drain the whole system and refill with new inhibitor?

 

[JohnD]

sounds unlikely to me. If he was in the habit of putting it in, he'd know what sort. He'd be buying it every month.

I'd assume none in and add Sentinel.

Is it a sealed system or is there a Feed & Expansion tank in the loft?

 

[JSM]

Hi JohnD,

It is a sealed system. He definitely put some in but I think he 'borrowed' it from his employer (the council) so he hasn't a clue what it was. Says he just put in what was lying in the van!

 

[JohnD]

very odd.

Maybe it was a rebranded stuff the council got under contract.

I use Sentinel these days in preference to Fernox (I am a householder not a pro) but these are the top two brands and widely available. It will only cost you about £15 for a litre unless you have an unusually large house and need more (I have a 3-storey house with 10 rads and cylinder plus F&E, with a water content of less than 100 litres all inclusive (measured at 19 gallons). the chemical is supposed to be at 1% or greater concentration.

You will probably have to use the injected stuff from a tube which i think works out a bit more expensive, as you have no F&E tank, but a sealed system is less prone to corrosion anyway

Hang or stick the label on the boiler or filling loop. You are unlikely to need to drain it again in future unless something goes wrong, but can top-up with the same type e.g. if you take rads off to redecorate

 

[JSM]

Hi JohnD,

Thank for that. The thing is everything I have read says you should not mix different brands and obviously there is something in already hence the plain to drain it. How often should it be renewed in any case?

 

[JohnD]

Yes, OK to drain it this time, but it will (should) last for years unless you drain, or get a leak, or need to top up the water.

It is possible to buy a test kit that checks inhibitor strength,
http://www.uk-plumbing.com/sentinel...4.html?zenid=1c2803e831447a649a8beda8f9074333
but personally I'd leave it 5 years before thinking about topping it up. There is an old method that Fernox used to recommend, involving a glass jar and a steel nail, but that amateur method is frowned on now. One of my neighbours tips in a litre every year, but that sounds excessive. One of the pros may know better.

Or you could ask the boiler engineer to check inhibitor strength when it gets serviced (the test kit is about £20 for ten tests)

 

[JSM]

Hi JohnD,

That's a brill idea! I'll get a test kit and if it shows everything okay that is fine. If not, then at least I'll know I am doing the right thing in draining and re-filling - and I won't make the same mistake again.

Thanks for all your help - greatly appreciated!