CH drain down help

[dcm017]

Hopefully posted in the correct forum!

Plumbing advice for a novice please. I have followed this forum for a while but my level of knowledge is limited so haven’t contributed.

I could get a plumber in but it’s something I ought to be able to do myself. I have always been keen on general DIY (woodworking mainly) but with a busy desk job I never had time and always ended up paying someone to do what I really wanted to do myself. Since I retired a few years ago I have the time and am always learning. I did attend a plumbing evening course but that was stopped in the 2020 lockdown and I haven’t (yet) gone back. I learned how to bend and join pipes and fit basins and toilets, but I never got as far as central heating!

I need to drain down my central heating system so that I can replace a radiator. The old radiator has corroded and leaks so I have bought a replacement from Screwfix which fits the space perfectly. The procedure looks straightforward but unfortunately the lockshield valve has jammed open and my attempts to close it have resulted in shearing the top off. So I need to replace it and hence the need to drain down the system.

It’s a fairly old bungalow and the plumbing has probably had changes over the years. The central heating system is gravity fed and we have a standard CH boiler. There are two drain valves in the cupboard next to the hot water tank. I don’t know which I ought to fit the hose to. I attach a couple of photos. I am hoping that someone experienced will look at it and say it’s obvious and give me the answer! It was suggest to me that the left hand valve might well be used for a separate isolated zone.

Maybe I am overthinking it and I should open and drain both valves.

Thanks in advance.

 

[aet1]

There really ought to be a drain off on the lowest radiator pipe, usually hidden under a radiator. Like this one, but I hope without cobwebs and paint falling off.
This style is designed to leak on the floor when a hose is fitted. Put down lots of old towels (even new ones of wife is out, but they will probably be black soon). A cooking tray is useful too. Then fit hose, put something a few cm high under the hose when it is still over the towels, water comes out the valve where you undo it, this is helps because the water will run along the outside of the hose so it can soak the new carpet. Just loosen the valve, last thing you want is the whole screw part flying out.

 

[aet1]

There really ought to be a drain off on the lowest radiator pipe, usually hidden under a radiator. Like this one, but I hope without cobwebs and paint falling off.
This style is designed to leak on the floor when a hose is fitted. Put down lots of old towels (even new ones of wife is out, but they will probably be black soon). A cooking tray is useful too. Then fit hose, put something a few cm high under the hose when it is still over the towels, water comes out the valve where you undo it, this is helps because the water will run along the outside of the hose so it can soak the new carpet. Just loosen the valve, last thing you want is the whole screw part flying out.View attachment 158056

I think that one like mine in the first picture should do the trick, but that valve to its left might be a replacement for one too.
I expect you have two tanks, the small one is for the central heating.
Be careful taking the old radiator off, when they drain some water is always left and it is black and stains.
If you have the time it's a good time to do what is left for a rainy day, run water through the system to flush out some of the rubbish and put some inhibitor in the tank before you refill it.
One of the solenoid valves has HW on it, I think you have a S plan system so the one near the floor would control the heating.
Of course I might be taking a load of rubbish, others, I am sure, put me right. I am not a plumber, but over the years have had some experience with central heating systems.
Best of luck. ( It's always best to turn off the main stopcock too, just in case the one to the tank leaks)

 

[dcm017]

I think that one like mine in the first picture should do the trick, but that valve to its left might be a replacement for one too.
I expect you have two tanks, the small one is for the central heating.
Be careful taking the old radiator off, when they drain some water is always left and it is black and stains.
If you have the time it's a good time to do what is left for a rainy day, run water through the system to flush out some of the rubbish and put some inhibitor in the tank before you refill it.
One of the solenoid valves has HW on it, I think you have a S plan system so the one near the floor would control the heating.
Of course I might be taking a load of rubbish, others, I am sure, put me right. I am not a plumber, but over the years have had some experience with central heating systems.
Best of luck. ( It's always best to turn off the main stopcock too, just in case the one to the tank leaks)

Many thanks of your thoughts on this. I have the towels/drip tray ready! It's all near the front door of the bungalow and messed up carpets are not a problem as I will be replacing carpet tiles shortly anyway - after the plumbing sorted. All radiators are at the same level so draining will probably be quite slow. I will look up "S plan system"!

 

[Nail]

If you want to speed the draining, take the bleed valve out of the rad your replacing.

If your other rads are ok and depending how your loop works, you could lock them all off to save some water in the system.

 

[dcm017]

If you want to speed the draining, take the bleed valve out of the rad your replacing.

If your other rads are ok and depending how your loop works, you could lock them all off to save some water in the system.

I hadn’t thought of locking off other radiators. To work out the loop would take some detective work though. The rogue radiator is almost the furthest away from the drain valve.

 

[Nail]

It depends on if you want to take advantage of the one rad change to clean and change all the water or not.

Have you got a mag clean in the system? Maybe add one now….

 

[Stuart Moffat]

I would also suggest that once you think you have emptied the radiator, ther will still be probably horrid water still in there. If you haven’t got any blanks to keep the nasty stuff in there til it’s outdoors, carefully turn it upside down whilst keeping it as level as you can (having first closed off the bleed tap!).

 

[dcm017]

I would also suggest that once you think you have emptied the radiator, ther will still be probably horrid water still in there. If you haven’t got any blanks to keep the nasty stuff in there til it’s outdoors, carefully turn it upside down whilst keeping it as level as you can (having first closed off the bleed tap!).

Thank you for the advice. I expect that the water coming out will be a very muddy colour so some flushing out will be needed. There is what appears to be a filter with Spirotech stamped on which I think deals with sludge so I will clear that out.

 

[Bingy man]

Find the small top up header tank and isolate the mains supply to it , if there is no stop tap or isso valve then tie the ball valve up so it can’t let in water . Turn the system off at the clock or timer . The valves in your pictures with the silver boxes on need to be opened manually and locked off ( small lever on one side ) pull back lever against the spring and push lever up into the cut out . Attach a hose to a drain off from the radiator circuit and open the valve ( anti clockwise ) be aware if your system is old and not been drained in a long time then the washer in the drain off can stick to the seating so get a couple of spares . If this happens the water will very slowly drain out of the system. Assuming all is going to plan you should see water gushing from the open end of the hose ( best placed into a foul drain) you can now open the vents to each radiator ( don’t remove completely) Allow all rads to drain and close the radiator vents - don’t over tighten. With trays at each end of your leaky rad you can now disconnect each end - as above expect black or orange sludge and protect your carpets . Pet training pads are ideal as they will absorb water . Remove rad valve ( change both) and fit new rad as reqd . Depending on the age of existing rad you may have to fit the new rad brackets and calculate their position so your new rad lines up with the existing valves but as you have drained the system you can make any alterations to the pipe work. Once everything is re connected turn the valves to the new rad off and you are confident that everything is sealed and tightened up Check all rad vents are off including the drain off that you drained from ( replacing the washer if in any doubt ) you may also have a vent point on the hot water circuits to the hot water cylinder. Check the top up tank is clean if not remove any rubbish ( sludge or insulation etc) Restore the water supply to the top up tank and allow water to re enter the system. Check for leaks constantly as you fill the system by opening the rads vents and letting out the air until it turns to water - a cloth to catch any drips is essential. Continue until all rads are full and check for vent points on hot water cylinder and vent out any air as required. Release the manual levers from the two zone valves and clean out the spirotech into a bucket . The cap is the key to open the drain valve . A couple of blasts should clear out any sludge . Check all rads for leaks and finally open the valves to the new radiator and vent out the air to fill it . Check for leaks and turn heating on and allow it to heat up -again check all rads are heating up and circulating and that you also have hot water. Assuming all is well with no leaks and rads all hot then give yourself a pat on the back and consider what to spend the several hundred pounds on you have just saved . Good luck

 

[dcm017]

Find the small top up header tank and isolate the mains supply to it , if there is no stop tap or isso valve then tie the ball valve up so it can’t let in water . Turn the system off at the clock or timer . The valves in your pictures with the silver boxes on need to be opened manually and locked off ( small lever on one side ) pull back lever against the spring and push lever up into the cut out . Attach a hose to a drain off from the radiator circuit and open the valve ( anti clockwise ) be aware if your system is old and not been drained in a long time then the washer in the drain off can stick to the seating so get a couple of spares . If this happens the water will very slowly drain out of the system. Assuming all is going to plan you should see water gushing from the open end of the hose ( best placed into a foul drain) you can now open the vents to each radiator ( don’t remove completely) Allow all rads to drain and close the radiator vents - don’t over tighten. With trays at each end of your leaky rad you can now disconnect each end - as above expect black or orange sludge and protect your carpets . Pet training pads are ideal as they will absorb water . Remove rad valve ( change both) and fit new rad as reqd . Depending on the age of existing rad you may have to fit the new rad brackets and calculate their position so your new rad lines up with the existing valves but as you have drained the system you can make any alterations to the pipe work. Once everything is re connected turn the valves to the new rad off and you are confident that everything is sealed and tightened up Check all rad vents are off including the drain off that you drained from ( replacing the washer if in any doubt ) you may also have a vent point on the hot water circuits to the hot water cylinder. Check the top up tank is clean if not remove any rubbish ( sludge or insulation etc) Restore the water supply to the top up tank and allow water to re enter the system. Check for leaks constantly as you fill the system by opening the rads vents and letting out the air until it turns to water - a cloth to catch any drips is essential. Continue until all rads are full and check for vent points on hot water cylinder and vent out any air as required. Release the manual levers from the two zone valves and clean out the spirotech into a bucket . The cap is the key to open the drain valve . A couple of blasts should clear out any sludge . Check all rads for leaks and finally open the valves to the new radiator and vent out the air to fill it . Check for leaks and turn heating on and allow it to heat up -again check all rads are heating up and circulating and that you also have hot water. Assuming all is well with no leaks and rads all hot then give yourself a pat on the back and consider what to spend the several hundred pounds on you have just saved . Good luck

Thank you for such a comprehensive reply. I will be doing the work this weekend with far more confidence than I had when making the original request. Much appreciated.

 

[pe2dave]

Watching a plumber drain my system, he made me laugh. The drain was 3 or 4" from the floor, i.e. no room for a bucket (I guess he didn't have a tube).
Used a 'strong' plastic bag to drain the system, since it adapted to fit the space!

 

[Bingy man]

Thank you for such a comprehensive reply. I will be doing the work this weekend with far more confidence than I had when making the original request. Much appreciated.

That’s fine just take it step by step and don’t rush - it was quite late last night when I read your post and recall you live in a bungalow- it’s very common for the system to have vent points in the loft - usually twin vents for the radiator legs - worth checking for before you start - if fitted you would open these after a few minutes of starting to drain the system and then vent the rads after a few minutes. . Ps when all done and no leaks drain the system again until the header tank / top up tank is empty and add a litre of inhibitor ( sentinel or fernox etc ) refill system and vent rads and any other vents in loft etc and its job done . The inhibitor protects the system.

 

[pe2dave]

(And don't forget to close the drain down plug ;-) )
(Yes, I did!)

 

[Bingy man]

Watching a plumber drain my system, he made me laugh. The drain was 3 or 4" from the floor, i.e. no room for a bucket (I guess he didn't have a tube).
Used a 'strong' plastic bag to drain the system, since it adapted to fit the space!

I’ve used a combination of a drain hose , lengths of plastic waste pipe and guttering to drain a system in on the 3 rd floor of a block of flats - if it gets the job done I’m all for it .

 

[andy48]

If you have a small tank in the loft (a Feed and Expansion (F&E) tank), I'd strongly recommend cleaning it out before draining the system. If you don't you will wash all the muck in that tank into your pipework and potentially the boiler. Isolate the supply (turn the water off or tie up the float valve arm) and use a bucket and sponge(s) to clean the tank out. The water is likely to be filthy and contain a significant amount of solids.

 

[user 35906]

If your feeling keen switch off the heating controls get a central heating bung kit or cobble something up) to seal the expansion pipe that terminates over the feed and expansion tank and seal the cold feed outlet in the same tank.
clearing a space under the leaking rad and pull back carpet if possible, put a plastic dust sheet and rags down under rad and with a shallow bowl under the easiest joint to loosen catch the water until it stops or almost stops (usually only a few pints) remove the dodgy valve and replace with the new valve that is turned off. Move to wheel head valve or TRV at the other end and repeat, then change the rad at your leisure. I used to use bungs all the time and they saved me hours draining down and bleeding afterwards and you keep the inhibitor and stale water in the system rather than filling with fresh oxygenated water to cause more rusting.

 

[Bingy man]

I think bungs are extremely helpful and save a lot of time if you’re experienced in using them . The o p is not that confident so draining the system will be safer for him . I’m sure at some point you have had a bunged system fail for one reason or another. Also the act of draining the system will teach him more about how his system works and will help him if in the future he needs to re - drain the system . Best he learns to walk first and run later -imho

 

[Richard_C]

I normally do this sort of thing myself, but last year we had a big job done by proper people -new boiler, new trvs, pump, hw tank, couple of replacement rafiators. Drain down valve was in a silly place in carpeted living room, so the wise plumber fitted 2 new ones while the system was empty. One on the kitchen rad by the back door, one on the hall rad by the front door. Why didn't I think of that 20 years ago?

So just have a think, is there anything else you could do while it's all empty?

 

[pe2dave]

I normally do this sort of thing myself, but last year we had a big job done by proper people -new boiler, new trvs, pump, hw tank, couple of replacement rafiators. Drain down valve was in a silly place in carpeted living room, so the wise plumber fitted 2 new ones while the system was empty. One on the kitchen rad by the back door, one on the hall rad by the front door. Why didn't I think of that 20 years ago?

So just have a think, is there anything else you could do while it's all empty?

flush it out 'properly' and add fernox?