Flushing the central heating system

[Nas1]

Hi guys,

New here so nice to meet you all. So to get straight into it I’ve stumbled upon a little issue. I decided to test run my central heating in prep for the winter to come but noticed 1 of my radiators doesn’t seem to be getting hot. Well, it gets warm to the touch but only around the top of the radiator and entry. The feed copper pipe is very hot but the return end is cold. This particular radiator has not really been used for the last 2 years as the bedroom was never in use thus having the valves closed for this radiator. However this winter that bedroom will be in use and so I need this radiator working. So I’ve been working through a little list to try and bring this into life by trying the following:
- Bled every radiator in the house. Nothing.
- Closed every radiator in the house except the one in question. Nothing
- removed radiator from wall took it into garden stuck a hose with running water into both feed and return ends, a lot of black water came out and eventually clear water followed. Refitted the radiator, bled and filled the pressure of the boiler and ran the system again. Same problem feed pipe gets very hot but water in the radiator is luke warm and only at the top of the radiator, the bottom right of the radiator at the return is cold and so is the pipe.
- tried rebalancing, no luck
- replaced lock shield valve on radiator, no luck
- checked trv valve, pin opening closing fine, I even tested this valve when the radiator was off and opening the trv resulted in water gushing all over the carpet lol

So after trying all of the above I’ve come to the conclusion it’s a faulty radiator (I am open to more suggestions in trying to bring my old radiator back into life)

Moving on, I’m planning on buying a replacement radiator from screwfix and I am thinking to do a complete system flush in the process. Now I’ve seen some threads on adding mains to the return/feed pipes under the boiler and then isolating the boiler from the system and then using the main water to circulate around the central heating system and dump into a drain. Unfortunately the pipework under my boiler is really inaccessible and trying to add/remove to the pipework will be an absolute ball ache having to potential remove some kitchen cabinets. So I am here trying to find alternative and gain guidance from you learned lot! My first question is, seeing as I will have the 1 radiator off the wall can I use the exposed return and feed pipes to flush the whole system? By this I mean connecting a mains water hose to the return pipe and another garden hose pipe to the feed pipe which leads into my toilet and allow the mains connected return pipe to just circle around the system and exit into the toilet? Would I still need to isolate the boiler for this or could I have the boiler part of the flushing process?

Second question is again using the exposed return and feed when the faulty radiator is off the wall. Can I close the feed valve on this whilst connecting a garden hose to the return side and exiting into the toilet and then using the fill valve under the boiler that is normally used to fill the system and increase the pressure of the boiler to flush the system and exit at the hose pipe going to the toilet? I hope that makes sense!

Feedback would be much appreciated and I look forward to hearing your responses

 

[Mottie]

Can I close the feed valve on this whilst connecting a garden hose to the return side and exiting into the toilet and then using the fill valve under the boiler that is normally used to fill the system and increase the pressure of the boiler to flush the system and exit at the hose pipe going to the toilet? I hope that makes sense!

The fresh water will probably take the easiest path through the system and not circulate all radiators. When I flushed mine, I removed all rads one by one and flushed out with a hose outside. Half fill rad, give it a good shake, empty out, rinse and repeat. Then drain and fill system. Run system, drain, refill until running clear. Then add some X400 cleaner in the system, run for a few days. Drain, fill, flush, repeat. When you’re happy it’s clean, add some inhibitor with the final fill. Time consuming but worth it. Oh, and fit a magnetic filter if you don’t already have one. That’s how I did mine anyway.

 

[Nas1]

The fresh water will probably take the easiest path through the system and not circulate all radiators. When I flushed mine, I removed all rads one by one and flushed out with a hose outside. Half fill rad, give it a good shake, empty out, rinse and repeat. Then drain and fill system. Run system, drain, refill until running clear. Then add some X400 cleaner in the system, run for a few days. Drain, fill, flush, repeat. When you’re happy it’s clean, add some inhibitor with the final fill. Time consuming but worth it. Oh, and fit a magnetic filter if you don’t already have one. That’s how I did mine anyway.

Thanks for the reply. The radiators in my system are around 3 years old, even the pipework is around the same age. Can I use my method in question to clean the return and flow pipes only whilst closing off all radiator valves? The problem is I don’t have a magnetic filter on my boiler so im thinking there must be something floating around

 

[Mottie]

The radiators in my system are around 3 years old, even the pipework is around the same age. Can I use my method in question to clean the return and flow pipes only whilst closing off all radiator valves?

I don’t know how your system is plumbed so I can’t comment on that. A three year old sealed system shouldn’t really have much much inside it. Mine was dirty because it was a 30 year old previously open vented system.

 

[lostinthelight]

When you flush , did/do you manually activate the zone valves.

 

[dilalio]

Sounds more like blocked return from that rad.

 

[terryplumb]

With the radiator removed ,open the return valve and let water run from it into a bucket ,see if there is a full, strong flow.

 

[Nas1]

With the radiator removed ,open the return valve and let water run from it into a bucket ,see if there is a full, strong flow.

Hi yes, when I removed the rad I opened the return and water shot into a bucket at a pretty decent pressure it only lasted 10 seconds as I’m guessing the pressure in the system dropped rapidly but there was murky water coming out, wasn’t thick and sludgy just dark in colour

 

[Nas1]

Sounds more like blocked return from that rad.

When I took the radiator outside and hosed it… clear water was coming out from the other side

 

[Nas1]

When you flush , did/do you manually activate the zone valves.

Sorry I’m not quite sure what you mean by this?

 

[terryplumb]

Hi yes, when I removed the rad I opened the return and water shot into a bucket at a pretty decent pressure it only lasted 10 seconds as I’m guessing the pressure in the system dropped rapidly but there was murky water coming out, wasn’t thick and sludgy just dark in colour

You should do the test again ,keeping pressure topped up whilst water runs out the return valve for on full minute. If there is a severe restriction in the return pipework the water will not flow fully.

 

[Nas1]

You should do the test again ,keeping pressure topped up whilst water runs out the return valve for on full minute. If there is a severe restriction in the return pipework the water will not flow fully.

the radiator in question is in a room on top of the kitchen where the boiler is so the pipework from the boiler to this radiator is probably less than 4m

 

[terryplumb]

That's all very well ,but you are not getting any flow through the radiator .if water flows strongly through both valves for 1 minute that proves the pipework isn't blocked. You Told us that water flows in one side of the rad ,and out the other side when a hose pipe is applied to it ,so the rad itself isn't blocking flow through it.
It sounds like there is an obstruction in the pipework,and probably on the return.

 

[Nas1]

That's all very well ,but you are not getting any flow through the radiator .if water flows strongly through both valves for 1 minute that proves the pipework isn't blocked. You Told us that water flows in one side of the rad ,and out the other side when a hose pipe is applied to it ,so the rad itself isn't blocking flow through it.
It sounds like there is an obstruction in the pipework,and probably on the return.

I see, I will take the rad off the wall again and open the return valve. Should I keep the fill open under the boiler whilst I do this so water continuously comes out the opened return valve?

 

[terryplumb]

Yes ,the system pressure needs to be maintained,so a second person attending to that whilst you observe the water flowing from the valve would be ideal.