Power flush

[Dee]

Estimated cost to power flush of 19 rads? In Suffolk?

Edited Monday at 15:25 by Dee

[JohnMo]

Ask a plumber?

[Dee]

I have! None have bothered to respond!!

[JohnMo]

Ask others? Are you talking to them? Phone them.

[Onoff]

[Nickfromwales]

20 hours ago, Dee said:

Estimated cost to power flush of 19 rads? In Suffolk?

Any reason to flush? You’ve drained this down a number of times and have some new valves here and there?

 

Water still grotty, or just cool spots on rads? 

[Onoff]

Power flushing won't necessarily work if your boiler is goosed. 

[Dee]

The boiler is 2 yrs old.

Only drained fown once in 20yrs. The last rad I took of was very black so just assumed a good flush would eliminate one less question mark...?

One rad is very temperamental. I'm genuinely too scared to run the heating too long to rebalance due to cost.!

[marshian]

17 minutes ago, Dee said:

The boiler is 2 yrs old.

Only drained fown once in 20yrs. The last rad I took of was very black so just assumed a good flush would eliminate one less question mark...?

One rad is very temperamental. I'm genuinely too scared to run the heating too long to rebalance due to cost.!

cost of a power flush buys a lot of gas at 6p per kWh - if a power flush us lets say £500 you’d be better of using it to purchase 8500 kWh of gas - that’ll more than cover most of the winter needs.

 

 

[Onoff]

1 hour ago, Dee said:

The boiler is 2 yrs old.

Only drained fown once in 20yrs. The last rad I took of was very black so just assumed a good flush would eliminate one less question mark...?

One rad is very temperamental. I'm genuinely too scared to run the heating too long to rebalance due to cost.!

 

You should really have had a power flush at the time of the new boiler maybe? A cruddy old system can as I understand it block even a newish boiler. 

 

Old man had BG install a new boiler and they didn't flush the old system first. Had repeated issues thereafter. Changed multiple parts and at one point even removed the mag filter they had previously fitted. Utter farce tbh.

[SimonD]

1 hour ago, Dee said:

The boiler is 2 yrs old.

Only drained fown once in 20yrs. The last rad I took of was very black so just assumed a good flush would eliminate one less question mark...?

One rad is very temperamental. I'm genuinely too scared to run the heating too long to rebalance due to cost.!

 

As @Onoff says, the system should be flushed as part of a boiler installation. Many boiler slingers will just do a chemical flush or nothing at all.

 

Whilst I always complete a flush when installing new boilers if someone I haven't done an install for asks me, I usually send them to British Gas as they used to have a lifetime guarantee for their flushing jobs.

[Nickfromwales]

@Dee, who fitted the boiler and did they flush it? 

[Onoff]

I had a Vaillant boiler in a rental with BG's top cover package for years. It was annually serviced by them along with multiple call outs and failures along the way. Not once did any of the engineers mention there was no mag filter fitted or recommend doing so. It got to the point different BG engineers were saying different things. One would order parts then another turn up to fit them saying they were the wrong ones. Another did suggest a power flush might work. 

 

I got so fed up I outed BG and employed a family friend to fit a new boiler a lot cheaper than BG. He did attempt to power flush the old system first to cure the old boiler but to no avail. At the outset he said he'd attempt it but it was unlikely to do much. Think he charged around £300 for the flush. He did add cleaner & leave the apprentice there all day with the flush rig running saying he wanted to see "clear water" running out of it before he called yay or nay on the boiler.

 

Sure he said modern boilers have quite a small heat exchanger that's prone to blocking which is why the system must be kept clean and have inhibitors in it. Something too about, again modern,heat exchanger materials being prone to corroding / blocking.

[Dee]

On 17/11/2025 at 15:47, JohnMo said:

Turn on your problem radiators and make sure they have no air trapped - so bleed with TRV open.  Can you force the radiator hot by closing off the other radiators via the TRVs?  So the only flow is directed to the cold radiators?  If not your may have bigger issues than simple balancing.  Assuming they get hot, the system isn't blocked up.

 

So now you have two options, pump set at too low a setting and not enough head to get to the issue radiator and/or balancing. dT that is big would indicate too little flow going through a particular radiator, low dT too much flow 

 

I would have a look at all the radiators to see what sort of dT is occurring across the radiators, they should be similar - do this with all TRVs open to get a sound starting point without adjusting anything.

 

11 hours ago, Nickfromwales said:

@Dee, who fitted the boiler and did they flush it? 

Local company fitted but didn't do a flush. Fell out with him big time as turned out over weeks we were being slowly gassed!! 

[Nickfromwales]

4 hours ago, Dee said:

 

Local company fitted but didn't do a flush. Fell out with him big time as turned out over weeks we were being slowly gassed!! 

Did you report it? 

[Temp]

I think I would drain and refill the system, possibly twice, then run the heating overnight and do one more drain and refill adding Fernox F1 or similar next day.

 

Ideally when you drain it measure the volume by filling and emptying bucket so you can calculate the exact volume of Fernox needed. Overdosing is OK though.

 

[marshian]

1 hour ago, Temp said:

I think I would drain and refill the system, possibly twice, then run the heating overnight and do one more drain and refill adding Fernox F1 or similar next day.

 

Ideally when you drain it measure the volume by filling and emptying bucket so you can calculate the exact volume of Fernox needed. Overdosing is OK though.

 

 

On a system with 19 rads that's a good way to get very bored

 

Provided you are on a water meter - Easier way to get system volume is to empty the system with a full drain down - then when refilling read the water meter before and after to get system volume (best done when no-one else is at home so they don't flush a toilet or run a bloody bath!!!) and either make a small allowance for air trapped in system or allow yourself time to bleed out the air before reading the meter

 

In reality most of the inhibitors are supplied in a container with a recommended dose for 100 Litres so if system volume is significantly above 100 Litres add 2 bottles

 

My system is 151 litres so I add 2 bottles