Expert level power flushing tips

This section is meant for plumbers and the wording is meant to be technical


Central heating pump – Can/should you flush through the pump? It is never a good idea to flush trough a pump, it does not matter if it is internal or external to the boiler. Sure on a practical level you can get flow through the pump in both directions using a power flush machine even with the pump running. If the pump is on, you will be fighting the pump every time you flush in the opposite direction, damaging the coil. When it is switched off; the impellers turning in the flow created by the power flush machine induces a current in the coil of the pump (when a magnet moves inside a copper coil you get electricity). This charge feeds back into the boiler / wiring and can cause the boiler to mysteriously shut down within hours after the flush. Solution: If the pump is external to the boiler you can disconnect the neutral wire to the pump. This breaks the circuit and it can’t produce a current when you flush trough it. If the pump is internal to the boiler: Turn the power to the boiler OFF and close one of the valves on the flow/return to the boiler. There cannot be flow through the pump if you do this. When you are flushing trough the boiler, leave it electrically isolated while doing so.

Full bore connection (picture) – When you connect into a central heating pump, the connection is obviously “full bore”, but when you connect trough a radiator it is a common mistake to connect onto the radiator valves. Obviously it is easier to connect on them as they allow the radiator to be drained down without draining the system and connect into the system without draining the rest of the system, but the radiator valves act like strainers and the larger pieces of sludge or debris will be left behind in the system, to cause loads of unexplained trouble. It is not that uncommon to get a large solder bead out of systems when flushing. We have encountered some large solder beads. This 8mm ball (picture), which was stuck in the pump causing noises when it was running. If we did not connect “full bore” that ball would still be in the system causing trouble even though it has just been flushed and the system water is completely clean.

Where to put the machine – If possible, always put the machine in a shower tray or in the bath. When you are running around the house/flat it is common to forget the water supply into the machine ON, overfilling it and spilling over. When you have the machine in the bath or shower tray it does not matter how long it spills over as it can safely drain away, down the plug hole.

A condition called “Sludge flake” (picture) – The sludge is turned into large flakes, same size of the pipes it made in. They are big and heavy and rigid, they travel along the pipes until they get stuck in a narrowing. Then they back up one after the other and compact, blocking the radiator/s, boiler, pump impellers. They are very hard to remove and it’s not always that affective to power flush them out. It depends how bad it is. The block can be as much as 2 meters long. One of the indicators of this condition is, absolutely clean water in the system. Conventional wisdom tells you only power flush when the system water is dirty, but with sludge flake, the water was dirty until it all turned into flake and sank down leaving little or not sludge in suspension. Making water samples seem completely clean. They are normally only found in systems containing plastic pipes or rubber hoses. read more >>

Where to set up in the property – Bathroom or outside is best. Bathrooms are the easiest because the floor is water proof, you can put the machine in a bath or shower tray and you can easily fill the machine while dumping the dirty water down the toilet.

Micro bore systems – If you are new to power flushing avoid them completely, they are very hard to work on any standard power flush machines are too weak to push through the sludge problems on these systems. Results are always unpredictable.

Open vented systems – They always have more sludge than sealed systems and the sludge tend to be much harder / hardened as well.
The “H” connection (picture), where the down feed pipe and the vent pipe meet the return pipe, just before the pump, NEVER flushes completely clean. If you flushed a system and the flow problem is still there, cut this junction out and replace it - or - clean with screw driver. Cut at least 15cm up the vent pipe, 15 cm up the downfeed pipe and 15cm (in both directions) up the return pipe. You will need to make very sure you scrape out all hardened sludge, this is a very common problem that power flushing does rarely fix regardless of the chemicals or machine used.
Try to connect to the external pump for a “full bore” connection.
Make sure that the bathroom radiator is not piped into the hot water circuit, because connecting into it will cause you to only flush 20% of the system.
Make sure you get flow on every radiator, if you don’t find out why. Could be a one pipe system or one radiator is run off another.
If at all possible, take the head of the 3-port valve and operate the pin manually, it gives you more control for focussing flow. With 2-port valves, just operate the “manual” pin on the heads.
Flush the hot water circuit and radiators circuit separately if at all possible. Flushing both divides your machines flow and that causes the radiators not to get cleaned properly.
When you can the tank off, use compression caps for both the vent pipe and the down feed pipe (disconnect from tank and cap) because they can’t get pushed out by the pressure, like a “bung” or leak like a push fit cap. If you are using a bung or push fit cap, check them when you start the flush and keep on checking them.

TRV (Thermostatic radiator valves) - the plunger tend to get stuck on its seat and that blocks the flow and your flushing attempts. Remove the head and pull the pin up manually, be gentle they sometimes come out completely and leak.

Focus your flow – Focus your flow to just one radiator at a time, never divide the machine’s flow between more or with the hot water circuit (open vented systems), if at all possible. It will make sure that the radiator gets the best clean possible.

Always disturb the sludge in the radiator – Use a rubber mallet or whatever works well for you to disturb the flow in the radiator that you are flushing. If you don’t, the flow will just go over the top of the sludge and you will have cold spots.

Power flushing leaks – It is common to get leaks on radiator valves where the spindle enters the valve body. The fix is easy; just tighten the nut at the bottom of the spindle. There are not many other places you will get leaks on a day to day basis.

Dumping down the toilet – If it’s cold day outside, you need to make sure that you don’t crack the toilet by dumping hot water down it. You will need to slowly warm it up by dumping first cold water and progressively hotter and hotter water down it. Never ever dump down a toilet with a macerator (big white box behind toilet) connected to it. The sludge will fill it up and block it, burning out the motor.

Strong acids – Manufacturers will all tell you that their acids are the best / strongest. Remember that you are always the one taking the blame if it goes wrong. If you are using an acid that needs neutralising make very sure you have enough neutraliser, before you do the flush. If you are not sure if the PH is neutral or don’t have a meter / PH paper on you to check, continually fill your machine with fresh water while dumping the return / system water for at least 30 minutes. This will make sure that you have added enough PH neutral (fresh water) to the system that will neutralise the acid left in the system while having dumped as much of the acid down the drain as possible. It is common the have at leas 2 radiator taps leak on you when you flush with acid, even on a small system. That is why we recommend using standard sludge remover over acid if at all possible and especially if you are new to power flushing. There are situations where you will need to use acid as the system is so badly sludged up that it would be a waste of time using anything else. Make sure the risk versus the reward is worth it for you, as you alone are liable. Also be very careful around old toilets or ceramic bathtubs when using acids, they can damage the ceramic and cause visible stains.

Connecting into the pump on a combi boiler – You have to be very sure about your own abilities and the capabilities and reliability of your equipment. If you get a leak on the pump connector or pipe connections, the water goes straight onto the boiler electronics which will short out. When you do this, isolate the boiler electrically and don’t open the hot water while flushing. Actuating the diverter valve while your machine is running can damage the valve. It is good practice to isolate the water supply into the combi boiler so that, even if someone opens the hot water taps, the diverter valve will not actuate. If you need to clean the hot water / secondary heat exchanger, remove if manually and flush both sides while it is out. Still it might have to be replaced. To get guaranteed results, some plumbers replace the secondary heat exchangers over tryng to flush them.

Chemical cleaning – Adding a cleaning chemical to the system and draining it down without using a power flush machine to create higher flow rates; is mostly waste of time and money. This will only work on systems that are not experiencing any problems related to sludge, before the flush, and therefore would not experience any problems after.

Primatic systems – these systems cannot be power flushed safely unless you cap off the primatic cylinder. If you are not sure, don’t even try to flush it.



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