How to release water in combi boiler to repair a leakage？

[LLL]

1 分钟前，Nickfromwales 说：

是的 

Great, thank you! i'll buy this one and replace it. Do i still need to buy the " Fernox Hawk White Jointing Compound" AND "Brass olives"? 

[Nickfromwales]

34 minutes ago, LLL said:

Great, thank you! i'll buy this one and replace it. Do i still need to buy the " Fernox Hawk White Jointing Compound" AND "Brass olives"? 

No need for the olives, yet, as I hope the one you have on the pipe will be ok to save with the PTFE tape.

 

You will need to test the repair and new valve for a few days, and then drain down a little to put 1x new inhibitor chemical in, but don't put that in until you know you do not have to drain down again, or that goes in the bin and you have to buy more.

 

LINK

 

This is a corrosion protection chemical which goes into the system and stays there for life.

[marshian]

49 minutes ago, Nickfromwales said:

No need for the olives, yet, as I hope the one you have on the pipe will be ok to save with the PTFE tape.

 

You will need to test the repair and new valve for a few days, and then drain down a little to put 1x new inhibitor chemical in, but don't put that in until you know you do not have to drain down again, or that goes in the bin and you have to buy more.

 

LINK

 

This is a corrosion protection chemical which goes into the system and stays there for life.

 

I'd replace the olive and use less PTFE tape but I'm not a plumber or heating engineer like @Nickfromwales

 

Watch this and you'll see exactly what over tightening an olive does and why it causes leaks to get worse (PS his presentation style is awful and irritating but from a content perspective it's worth a watch)

 

 

I also prefer to use LSX rather than PTFE tape but either are pretty fullproof solutions to leaks from compression joints without excessive tightening

 

https://www.screwfix.com/p/fernox-ls-x-leak-sealer-50ml/23614

 

No idea yet on how to do an embedded link perhaps @Nickfromwales will share that secret

 

 

[Nickfromwales]

12 minutes ago, marshian said:

(PS his presentation style is awful and irritating but from a content perspective it's worth a watch)

He looks completely infectious... lol  I'll belay watching that.

 

12 minutes ago, marshian said:

No idea yet on how to do an embedded link perhaps @Nickfromwales will share that secret

 

Just click on the hyperlinky thingy-doo-dah at the top of the editor box?

 

12 minutes ago, marshian said:

I also prefer to use LSX rather than PTFE tape

That's basically a toothpaste tube filled with clear silicone?

[marshian]

50 minutes ago, Nickfromwales said:

That's basically a toothpaste tube filled with clear silicone?

 

Except that it doesn't go off like a cartridge of silicone - had my tube for nearly 10 years and it's still usable - which considering a normal cartridge of silicone is knackered after 6 mths makes me feel the product is a different formulation

[Nickfromwales]

21 minutes ago, marshian said:

 

Except that it doesn't go off like a cartridge of silicone - had my tube for nearly 10 years and it's still usable - which considering a normal cartridge of silicone is knackered after 6 mths makes me feel the product is a different formulation

Or that you do less plumbing than me, lol.

[marshian]

15 minutes ago, Nickfromwales said:

Or that you do less plumbing than me, lol.

Oh that for sure

[LLL]

11 hours ago, Nickfromwales said:

When the pressure is zero on the boiler gauge, the system and radiators will still be nearly 100% full, if they are not on the next floor up above the boiler.

 

You need to drain down the radiator you’re working on. Get one of these LINK and a radiator key LINK to open the vent at the top of the radiator. Until you open that, the water will stay in the radiator on vacuum. 
 

Drain out until there’s no more water to come out.

 

Then fit the new valve. You need to get some PTFE tape LINK to go around the olive on the pipe (where you fear you’ve ’broken’ the pipe). You know when you’ve done this as the leak goes from bad to very bad.

 

Applying this tape (10 turns) is to cover you from the olive having been crushed a little too much by over tightening with a spanner.

 

Smear some jointing compound over the threads, over the olive (after tape) and this will mean you get a good seal without having to go Hulk on the spanner again. For the next tightening up, go easy, and try it first. Then go tighter just a 1/4 turn at a time if a small leak begins to show.
 

 

The you close the vent at the top of the radiator.
 

Then you go to the boiler and test fill the system back up to 1.5 bar on the gauge to check for leaks. If all good after 30 minutes, then bleed the radiator vent to get the air out.

 

Then top the pressure back up (letting air out will make the pressure drop again on the boiler gauge) and run the radiators up to max temp for 30 mins and keep checking.

 

If all good, select a nice shirt and get to the pub to celebrate. 🍾 

thank you, Nick, again for your so detailed guidance, I really apppreciate it! I guess i can trun off all radiators to lock as much water inside the radiators so i can drain less water out. Also after i have fixed the leaking, and topup water, since the power is off, how can i know i will not topup too much or too less water? 

[marshian]

17 minutes ago, LLL said:

thank you, Nick, again for your so detailed guidance, I really apppreciate it! I guess i can trun off all radiators to lock as much water inside the radiators so i can drain less water out. Also after i have fixed the leaking, and topup water, since the power is off, how can i know i will not topup too much or too less water? 

 

You might require several top ups as you bleed air out of the system - that's just a consequence of introducing air into pipe work - it will find it's way to rads and as a result you will need to bleed them several times

 

 

[LLL]

thank you! I just watched the video of this guy, so good. He also introduced a way to replace the part without draining the boiler, just use the bleed to drain the single radiator, the water is less than i expected. Do you think, for a beginner, this is easier than drain the whole system throguh the filter on the boiler? BTW, the leaking is on the second floor and the boiler is downstairs, there are 5-6 radiators in  both upstairs and downstairs 

 

  

[marshian]

28 minutes ago, LLL said:

thank you! I just watched the video of this guy, so good. He also introduced a way to replace the part without draining the boiler, just use the bleed to drain the single radiator, the water is less than i expected. Do you think, for a beginner, this is easier than drain the whole system throguh the filter on the boiler? BTW, the leaking is on the second floor and the boiler is downstairs, there are 5-6 radiators in  both upstairs and downstairs 

 

  

 

I've done the same before but I think there are a couple of points to think about

 

1. The condition of the olive 

2. Possible need to PTFE tape or remove and replace the olive

3. Miss match on old nut to new fitting

4. First time..................

 

I'd drain down

 

[LLL]

thank you, just one question, i plan to buy this one, but if you look at my radiator, seems the part in his left hand will not be used? the one i plan to buy is this one, https://www.screwfix.com/p/flomasta-15mm-x-21mm-white-chrome-angled-modern-manual-radiator-valve-head-body/901fw seems the same, should i remove the part in circle? from my radiator, seems that part is not needed. also the nut, is it the right position? sorry this is my first time to deal with boiler, just want to make sure buy the right one. 

 

[LLL]

had a look of the video again, i think the green circled part is the part connecting with the radiator, I probably do not need to replace this part, so just use the part in his right-hand in the figure. 

[Nickfromwales]

9 hours ago, LLL said:

had a look of the video again, i think the green circled part is the part connecting with the radiator, I probably do not need to replace this part, so just use the part in his right-hand in the figure. 

Yup. 👍. 
 

Put some jointing compound on the faces that meet together of the two parts, and a little on the threads.

 

Joints should tighten smoothly, and not squeak like brass on brass does when dry.

 

I’d drain down and take your time to do the repair. Prob only adds 2-3 hrs more messing around but a more relaxed job then   

[marshian]

3 hours ago, Nickfromwales said:

I’d drain down and take your time to do the repair. Prob only adds 2-3 hrs more messing around but a more relaxed job then   

 

Like he said - plus the added issue of if you are hot swapping something and it's goes wrong (for whatever reason) you are in a whole heap of pain and stuck with your fingers in holes trying to explain to the significant other what the bloody hell they need to do to drain the system down so you can take your fingers off the bloody pipes - which is what I meant by point 4. First time.............

[Nickfromwales]

2 hours ago, marshian said:

Like he said

It is now I’ve edited it ffs. 
 

This poxy phone writes what it wants to. (expletive deleted) my version off, why don’t you ?!?!

 

Id be happy to go back to scratching this all into a bit of slate. 
 

Rant almost over ……

[LLL]

Thank you so much both. I have to say so lucky to have your guidance here, I have bought all required and plan to do tomorrow, hope everything goes smoothly - especially with your valuable guidance. 
 

separately, my boiler pressure drops to around 0.7, after top up to 1.3-1.5, in 2 weeks it drops to 0.7 and keeps stable. That happens before this leaking and I checked around did not find any major leak in the house, but not able to see under the floors. Do you know that could be caused by a leakage or system issues? Is there potential leaking in the crawl space, I could check and fix it together tomorrow. 

 

[LLL]

On 09/10/2025 at 19:02, Nickfromwales said:

Yup. 👍. 
 

Put some jointing compound on the faces that meet together of the two parts, and a little on the threads.

 

Joints should tighten smoothly, and not squeak like brass on brass does when dry.

 

I’d drain down and take your time to do the repair. Prob only adds 2-3 hrs more messing around but a more relaxed job then   

Hi Nick, I have followed the suggestion replaced the part, it works well and no leaking so far! I got hot water but heating seems not working properly, i can feel a bit warm on the radiator close to the boiler but the temp is not as high as expected, seems the boiler is not burning the heating or working at a very low power, there is a sign shown on the screen, can you please tell what does it mean and how to fix it? 

Edited Friday at 20:46 by LLL

[LLL]

On 09/10/2025 at 19:49, marshian said:

 

Like he said - plus the added issue of if you are hot swapping something and it's goes wrong (for whatever reason) you are in a whole heap of pain and stuck with your fingers in holes trying to explain to the significant other what the bloody hell they need to do to drain the system down so you can take your fingers off the bloody pipes - which is what I meant by point 4. First time.............

Could you please also have a look of the issue? thanks 

[Onoff]

According to ChatGPT:

 

https://chatgpt.com/share/68e973b3-9810-8006-85ab-ce163c5f9890

[LLL]

Just read the manual again, seems this is a standard procedure, it says "When the symbol appears alternately with the flow temperature, the siphon filling program is active. The condensate siphon in the appliance is filled" 

[Nickfromwales]

34 minutes ago, LLL said:

Just read the manual again, seems this is a standard procedure, it says "When the symbol appears alternately with the flow temperature, the siphon filling program is active. The condensate siphon in the appliance is filled" 

Yup. 
 

It’s doing an automatic “purge” of the air. 
 

One of WB more annoying features as when we were all tired and fed up after fitting the bastard things we had to wait for “it” to “decide” when we could go home lol. 
 

Sit and wait. Won’t be long !

[Nickfromwales]

56 minutes ago, LLL said:

I have followed the suggestion replaced the part, it works well and no leaking so far!

That’s excellent news   

 

However. 
 

 

 

Your advisory bill is now calculated at £7,366.00. 
 

Please send cash only.

 

And don’t say anything to the others as I would rather they didn’t know   

[LLL]

1 hour ago, Nickfromwales said:

That’s excellent news   

 

However. 
 

 

 

Your advisory bill is now calculated at £7,366.00. 
 

Please send cash only.

 

And don’t say anything to the others as I would rather they didn’t know   

Now everything goes back to normal, no leakage, and one radiator used to not warm now also works perfectly! This is the first time for me and I always worry about the situation can go beyond control and water is everywhere. It gives me confidence and I am sure I can change a radiator next time! Your guys suggestions are so valuable and exact - chatGPT talks a lot if you ask, but many rubbish. When you are up to the north, happy to buy a pint for you! Seriously, if I call someone professional to fix for me, how much I have to pay? Just want to show off to my wife today I saved £xxx for the family! 

Edited Friday at 23:12 by LLL

[Nickfromwales]

39 minutes ago, LLL said:

Now everything goes back to normal, no leakage, and one radiator used to not warm now also works perfectly! This is the first time for me and I always worry about the situation can go beyond control and water is everywhere. It gives me confidence and I am sure I can change a radiator next time! Your guys suggestions are so valuable and exact - chatGPT talks a lot if you ask, but many rubbish. When you are up to the north, happy to buy a pint for you! Seriously, if I call someone professional to fix for me, how much I have to pay? Just want to show off to my wife today I saved £xxx for the family! 

Happy days  

🍻