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Discuss Is powerflush really any better than chemical plus mains flush? (before boiler repair) in the Central Heating Forum area at PlumbersForums.net

Messages
19
Hello,
BEFORE
I cleaned the system last year with a mains flush. There was a little inky stuff and a bit of sludge at the very end when I emptied out the rad I took off the wall, but no rads have ever had cold patches. Most pipes are hep20 but I had small section replaced by copper 2 years ago (should the system have been flushed with new system cleaner after adding copper pipes? It was not)

NOW

Both heat exchangers are broken in my BAXI combi boiler. The plate exch got blocked and caused the boiler to bang. DHW slowed to a trickle and after some weeks it overheated the main heat exchanger which is now leaking out the condense pipe.

The gas engineer will replace both heat exchangers but he recommended I clean the system before he does the job.

I have filled the system with x400 and run it for a few hours and left the chemicals to work for a few days. I will top up with more x400 and then run it again for 2 hours. Then I will take off a radiator and connect one hose to mains water and the other hose going down the drain, then proceed to flush the system through with clean water in both directions.

I will then repeat with x800 cleaner with all rads closed, just to clean the boiler.

Is there anything wrong with my plan? Should I hire a powerflush machine (£120). What advantage is there in doing a powerlush other than it being quicker? With my manual method I can let the chemicals work for days, I can still heat the water and pump it round with the boiler and rinse it at mains pressure. Is this going to be good enough or should I hire a machine?

I don't have experience to know if a powerflush is worth it so a opinion from seasoned professionals would help me decide whether to shell out an extra £120 on what is already going to be a costly repair.

Does a powerflush push water round any better than the boiler's pump or mains pressure?

Thanks.
 

EvilDrPorkChop

Gas Engineer
Messages
702
Hello,
BEFORE
I cleaned the system last year with a mains flush. There was a little inky stuff and a bit of sludge at the very end when I emptied out the rad I took off the wall, but no rads have ever had cold patches. Most pipes are hep20 but I had small section replaced by copper 2 years ago (should the system have been flushed with new system cleaner after adding copper pipes? It was not)

NOW

Both heat exchangers are broken in my BAXI combi boiler. The plate exch got blocked and caused the boiler to bang. DHW slowed to a trickle and after some weeks it overheated the main heat exchanger which is now leaking out the condense pipe.

The gas engineer will replace both heat exchangers but he recommended I clean the system before he does the job.

I have filled the system with x400 and run it for a few hours and left the chemicals to work for a few days. I will top up with more x400 and then run it again for 2 hours. Then I will take off a radiator and connect one hose to mains water and the other hose going down the drain, then proceed to flush the system through with clean water in both directions.

I will then repeat with x800 cleaner with all rads closed, just to clean the boiler.

Is there anything wrong with my plan? Should I hire a powerflush machine (£120). What advantage is there in doing a powerlush other than it being quicker? With my manual method I can let the chemicals work for days, I can still heat the water and pump it round with the boiler and rinse it at mains pressure. Is this going to be good enough or should I hire a machine?

I don't have experience to know if a powerflush is worth it so a opinion from seasoned professionals would help me decide whether to shell out an extra £120 on what is already going to be a costly repair.

Does a powerflush push water round any better than the boiler's pump or mains pressure?

Thanks.
How old is your system?
 

EvilDrPorkChop

Gas Engineer
Messages
702
Is it barrier pipe?

If it's Grey HEP, it's possible it isn't barrier. If it's not then it'll draw in oxygen which has caused your corrosion.
 
Messages
19
Is it barrier pipe?

If it's Grey HEP, it's possible it isn't barrier. If it's not then it'll draw in oxygen which has caused your corrosion.
It is grey, but it is definitely the barrier version. A few years ago, I had a section under the bathroom replaced with copper because it will not be accessible after the bathroom floor is down. The system wasn't flushed after that, only refilled but it was not a huge area.
 
Messages
831
1. It would be useful to know which side of the plate heat exchanger was blocked.
1a. If the boiler primary side, then sludge may well be the issue.
1b. If the domestic hot water side, this could be caused by limescale. If the incoming cold can't remove the heat fast enough, then that could cause the primary side to overheat, with consequent impact on the primary heat exchanger.
2. If sludge is an issue, then I personally would advocate a powerflush, complete with agitation of the radiators. The chemicals are strong enough to require separate neutralisation once the process is complete, and I'm not sure if that is the case with ordinary system cleaners. It also does more for the pipework, and sludge often accumulates in lowest level horizontal pipes.
3. While green grant is correct in suggesting that most of the corrosion comes from the radiators, that sludge does move through the system, and can settle in pipework as noted above.
4. It has been shown that oxygen can pass through non-barrier pipe, whether with or without nitrogen or other trace gases in the air doesn't matter. Oxygen thus passes into the system through being dissolved in the water, and causes further corrosion of steel radiators, and thus generates additional magnetite sludge.
 
Messages
19
1. It would be useful to know which side of the plate heat exchanger was blocked.
1a. If the boiler primary side, then sludge may well be the issue.
1b. If the domestic hot water side, this could be caused by limescale. If the incoming cold can't remove the heat fast enough, then that could cause the primary side to overheat, with consequent impact on the primary heat exchanger.
2. If sludge is an issue, then I personally would advocate a powerflush, complete with agitation of the radiators. The chemicals are strong enough to require separate neutralisation once the process is complete, and I'm not sure if that is the case with ordinary system cleaners. It also does more for the pipework, and sludge often accumulates in lowest level horizontal pipes.
3. While green grant is correct in suggesting that most of the corrosion comes from the radiators, that sludge does move through the system, and can settle in pipework as noted above.
4. It has been shown that oxygen can pass through non-barrier pipe, whether with or without nitrogen or other trace gases in the air doesn't matter. Oxygen thus passes into the system through being dissolved in the water, and causes further corrosion of steel radiators, and thus generates additional magnetite sludge.
Due to COVID the engineer diagnosed the faults over the phone. I told him what is typed below. He will confirm the faults when he comes to carry out the work next week.

A bit more background:

About 2 years ago, the plate exchanger got blocked on the heating side with flakes/crumbs of black stuff. It was cleaned with water and put back and the water flow and temperature were fixed.

After about a year, the slow flow and banging noises returned and the boiler stopped working E133 (no ignition) so while I waited for the engineer appointment, I dosed each rad with x400 in and left for 3 weeks then flushed through in both directions from the mains tap water. The boiler was isolated during this to prevent debris being flushed into the boiler.

When the engineer came, he found the ingition wire needed cleaning and the boiler fired up. The hot water was fast and hot without interfering with the plate exchanger so he decided not to remove and clean it as planned. He thought that flushing the system had solved the problem.

However, a few weeks later the banging returned with low flow and low temperature. I could not find a free engineer over the winter so I added x200 (silencer) but the problem got worse. I noticed the boiler losing pressure and needing a top up about once a week and then more frequently until it was every day.

I think some water was dripping out the pressure release pipe when the hot tap was being used but then it changed to the condense pipe dripping all the time.

Then it stopped firing up E133. The pressure relief pipe stopped dripping but the condense pipe was dripping.

Each time I refilled the boiler the condense pipe would empty the boiler within an hour (still not firing up). This was during freezing weather.

Fast forward to now. I dosed the system with x400 and poured hot water from the kettle into a radiator to warm the water a little and repressurised the boiler. Now it fired up again but was losing pressure via the condense pipe after a few hours. I have topped it up several times the same day and now a day later, it is holding pressure at 1.5 bar for over 24hours and no more pipes are dripping!

A new heat exchanger (expensive) was ordered to be fitted next week on the basis that the leaking from the condense pipe indicated a broken main heat exchanger. But now it is only losing pressure very slowly. What's going on?
 
Last edited:

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