Can I get away with just depresurisig the system?

[gorselands]

Old big house with two combi boilers - one for upstairs, one for downstairs.

The system for downstairs has one rad in the bathroom upstairs. So highest point on the circuit.

I had to fit a 2 new rads downstairs and whilst the system was drained decided to replace the one in the bathroom that was showing some rust on the bottom seam. I took it off only to realise the valve fittings/tails were 3/4 and I couldn't remove them (no flats). Probably damaged them trying to remove non existent olives. Gave up and fitted blanking caps.

Only managed it today after Googling (never seen them before) and improvising with a spline key and ratchet - easy. In the meantime I had to refill the system and get the heating on.

Today bought 15mm tails and new TRV

Now the question!! As the rad/pipes are at the highest point on the circuit, can I let the pressure out of the system either at the boiler or at a rad and will the water stay in the pipes allowing me to fit new rad, tails and TRV or is it another drain down? Is there such a thing as a partial drain down?

Sorry this is so convoluted but I hope I have explained myself well enough.

Many thanks - Mike

 

[petertheplumber12]

If you release pressure at rad AFTER you have gone to boiler and turn OFF the flow and return pipes valves under the boiler, this will save expansion vessel depressurising unnecessarily, with boiler switched off of coarse. then there will be very little water in the system to remove. I don't agree with using the pressure relief valve to depressurise, it can make them start to leak. And good luck. use ptfe tape to seal 1/2" thread into rad.

 

[petertheplumber12]

I very rarely drain down to alter pipe work on heating circuits, once it's sealed it can't go anywhere.

 

[dcawkwell]

You don't need to drain the whole system down.
If working on radiators upstairs you only need to drain down until
there is no water in the radiators upstairs.
But I rearly care. I open the drain valve and leave it open I then start work.
I then refill once complete.
It doesn't really matter that much.

 

[gorselands]

That's great. Thanks very much. I can go ahead with some confidence now.

Just a thought, how many winds of PTFE are generally used. I was reading somewhere that one guy used 10 to 15. It surprised me as I generally use about three plus a bit of silicone grease on threads. And, do you wrap round the olive?

Mike

 

[Whitespirit66]

3 turns not enough, 15 is overkill. Approx 7 or 8 turns clockwise (looking onto the open end of the tail.

No PTFE on olives, or you'll make it a dead giveaway that an amateur was at work. Just a smear of Boss White or similar pipe jointing compound.

7 turns and clockwise on here -

 

[gorselands]

Again, many thanks for info and the link. It's the small details that make the job.

Mike