Flush radiators using filling loop

[Frogwell]

Morning All,

Long time lurker, first time poster - Hello

It has become time to flush my radiators, on account of them having patchy heating. Being of cheap nature, I'm going avoid paying someone else to powerflush them and see how badly I can mess things up myself. I have a decent amount of DIY plumbing experience (that's not to say I've been doing it right of course!) but my modern central heating experience is fairly limited - changed the pump, diverter valve, PCB and a few other bits and bobs over time, but not much else.

I have a nine year old external oil fired Worcester Bosch 18/25 combi boiler powering seven radiators and I wish to flush the radiators using the method in this thread: https://www.diynot.com/diy/threads/how-to-flush-a-heating-system-with-mains-water.38902/

I have a couple of questions though - the article says to close the boiler circuit - presumably that would be done with the valve shown in the picture below? (I actually need to replace that valve as it doesn't seem to do anything.)

The next question would be where to drain. I've had engineers round when the boiler went wrong in the past and they both drained from two different points (see picture below), but they couldn't say why they did it from their chosen point and whether it was better than the other drain point - I think the basically used the drain point they saw first. Is there a difference between the two? Why does it have two in fact? Can I use either one?

Many thanks,

Mark

 

[Mottie]

Before you do that (or perhaps instead of doing that) why not remove your radiators, take them outside, empty them, flush through with a hose, half fill with water, shake 'em up, flush, repeat until you get clear water running out of them. That’ll get much more crud out of the system than just running cold water through them. You could then perhaps add some chemical flush when you refill, run the system for a while, drain and refill with fresh water a few times then add some inhibitor. I did that about 18 months after I had a powerflush and just before a new boiler was being fitted and I got a right load of crud out of the rads. I have a sealed system but if yours is vented, don’t forget to clean out the header tank too.

 

[Frogwell]

I did consider that, and I've not totally ruled it out, but as well as being cheap and I'm also quite lazy so I was hoping to get away with doing the minimum amount of possible

 

[Mottie]

Hmm. Cheap don’t normally go with lazy but good luck.

 

[Frogwell]

Very true, I'm probably not considered one of life's winners

 

[durhamplumber]

Very true, I'm probably not considered one of life's winners

You need some confidence flushing into your system dude.

 

[Madrab]

You will never be able to get a chemical mains/gravity flush to clean the system, especially rads with definite cold spots, anywhere near the same as taking them off the wall and hosing them out until it runs clear.

Dose the system with cleaner, run it for a few days, rads isolated and off the wall and flushed via every tapping while tapping the bottom middle with a rubber mallet.

Well inhibited and then a Mag filter, if none fitted, would be ideal.

 

[Hugh Jaleak]

The arrowed valve looks to me more likely to be an Non Return Valve, it may well be doing its intended job.

 

[oilboffin]

They are isolation valves you can flush using them and drain from the return line put cleaner in a week before then flush.Bob

 

[Gasguru]

99% of "patchy heating" I come across is due to poor balancing, incorrect pump and bypass settings diverter letting by etc.
Genuine sludge in radiators is very rare...if the system was that bad your plate heat exchanger would be causing issues.
Whilst the rads are still connected to the rad valves you will never get a sufficient flowrate to clear them out.