Flushing a 40 year old untouched heating system

[Topcat33]

I am having my 40 year old free standing boiler replaced with a new combi. This system was installed using fernox inhibitor from new and no work has ever been done on the water side and so it is the same water as at the start. (Apart from top up for bleeding)
It is a heating only boiler with an F and E tank (hot water supplied by separate multi point)
There are no cool areas on my radiators, but the water is slightly black on bleeding.
Does this need a power flush or just the chemical flush supplied with the new filter?
Also what if we put mains pressure through the feed pipe from the tank to the boiler, ran the pump and flushed it all out via the drain valve at lowest level, would that work?

 

[CountryFan]

so it is the same water as at the start. (Apart from top up for bleeding)

That sounds like Triggers broom. How can it be the same water if you’ve added water to top up? Therefore diluting any inhibitor that was added

Does this need a power flush or just the chemical flush supplied with the new filter?

Sounds like it may just need a chemical flush, but adhere to manufacturers recommendations in most cases for the warranty.

 

[Topcat33]

That sounds like Triggers broom. How can it be the same water if you’ve added water to top up? Therefore diluting any inhibitor that was added

Sounds like it may just need a chemical flush, but adhere to manufacturers recommendations in most cases for the warranty.

Ha, yes I thought that as I wrote it ‘I’ve ad this brush for 20 years”
Tank has a good concentration of inhibitor and topped up

 

[ChrisJP]

If you're putting in a combi boiler I think this will mean that there's no F&E tank and instead the radiator circuit will be under mains water pressure. If so, be prepared for some leaks!

 

[fixitflav]

I am having my 40 year old free standing boiler replaced with a new combi. This system was installed using fernox inhibitor from new and no work has ever been done on the water side and so it is the same water as at the start. (Apart from top up for bleeding)
It is a heating only boiler with an F and E tank (hot water supplied by separate multi point)
There are no cool areas on my radiators, but the water is slightly black on bleeding.
Does this need a power flush or just the chemical flush supplied with the new filter?
Also what if we put mains pressure through the feed pipe from the tank to the boiler, ran the pump and flushed it all out via the drain valve at lowest level, would that work?

Do you intend to use the HW function of the combi? That might mean a lot of pipe work mods. If not it would be simpler (and cheaper) to install a heat-only boiler, and keep the F/E tank and pump. And avoids the risk of putting mains pressure on an old system.

 

[Topcat33]

Do you intend to use the HW function of the combi? That might mean a lot of pipe work mods. If not it would be simpler (and cheaper) to install a heat-only boiler, and keep the F/E tank and pump. And avoids the risk of putting mains pressure on an old system.

Yes, getting rid of the 25 year old multi point as well, no worries about the plumbing, I’ve done a lot.
When you say “mains pressure” The boilers must have a governor to regulate the pressure going through the system as no mains pressure is the same. If it finds leaks I’ll fix it, no worries. ( I bet that comment could come back to bite me! )

 

[ChrisJP]

I guess you'll have to hope that leaks don't occur in inaccessible parts of the heating circuit - like under floorboards etc. What do you want to achieve by getting rid of the F&E tank and going over to mains pressure in your CH circuit even if governed? I'm a great believer in "if it ain't broke, don't fix it"!

 

[Johntheo5]

Yes, getting rid of the 25 year old multi point as well, no worries about the plumbing, I’ve done a lot.
When you say “mains pressure” The boilers must have a governor to regulate the pressure going through the system as no mains pressure is the same. If it finds leaks I’ll fix it, no worries. ( I bet that comment could come back to bite me! )

There may be a boiler low pressure trip but shouldn't be higher than 0.5bar so you can use a expansion vessel precharge of say 0.7bar and a filling pressure of 1.0bar which means the (downstairs) rads are only exposed to a very moderate pressure increase, they are at ~ 0.6bar from the F&E as is.

 

[Scally-Ho]

If that was my personal heating system, I'd remove every radiator in turn and after using a waterways brush, fully reverse flush with mains water hose until the water ran crystal clear.
As a general rule, never expose a heating system to mains water pressure because the radiators are not designed to withstand such pressures unless specifically manufactures as such.

 

[Stuart981]

If the system is oil or solid fuel and is working OK then I would probably just look for a more modern second hand replacement boiler and swap it over.

 

[JohnD]

You mention a new filter.

If you mean a magnetic filter, I'd add that before you do other work. Sediment will be dislodged and you want to trap it before it can accumulate in a new place.

It will continue trapping residue even after your chemical clean, though you'll see the amount reduce over time,

 

[fixitflav]

I guess you'll have to hope that leaks don't occur in inaccessible parts of the heating circuit - like under floorboards etc. What do you want to achieve by getting rid of the F&E tank and going over to mains pressure in your CH circuit even if governed? I'm a great believer in "if it ain't broke, don't fix it"!

My thoughts too. Starting from scratch maybe 50:50 between F/E tank and pressurised, but not if the tank is already there. And with pressurised, need to top up pressure every few weeks, but a F/E tank system looks after itself from one year's end to the next.

 

[DP]

I would not pressurise the system
Slightest weep or leak will show up as constantly needing topped up.
If this was my system, I would specify an Intergas combi boiler run as open vented- have done it a few times

Use mains to flush out the radiators with aid of rubber hammer. Fit an Addey Megnaclean and dose system with inhibitor

 

[Topcat33]

I guess you'll have to hope that leaks don't occur in inaccessible parts of the heating circuit - like under floorboards etc. What do you want to achieve by getting rid of the F&E tank and going over to mains pressure in your CH circuit even if governed? I'm a great believer in "if it ain't broke, don't fix it"!

My ch boiler is 40 years old my multi point is 25, my gas bills are 30% higher than average for my house I need an upgrade, thanks for everyone’s advice I have taken it all on board and will not be putting mains pressure to flush it, and am carefully considering my options. Thank you