Draining Central heating

10 Jun 2018
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United Kingdom
I am about to do some modifications on my central heating system. This will entail me draining down the system after adding some cleaner/ descale for whatever period specified. The boiler ( firebird popular 90 ) is in the garage. Its a 2 story house with open vented system. There's 2 options open to me for draining down at present. There's a long crawl under the house ( or stomach slide more like it) to a drain cock on the end of the main 22mm flow pipe. This is fitted with a short hose that is pushed out through an air brick and empty onto garden path. Other is the drain cock fitted to the bottom of the boiler. Last time I drained, I used the Boiler option, but it took hours to drain, and the drain cock leaked from the spindle. My question is, once I have the system drained this time, I want to fit a Tee into the flow or return pipes into the Boiler and use this as a drain off in future. Is there any difference in what pipe I use ? Flow or return ?.
The Tee would be 22mm x 22mm x 15 mm for the drain. Does it have to be a drain cock on the end of the 15MM Pipe. There would be an isolation valve fitted ( Ball lever or gate ) to the 15mm drain pipe. It just seems that every drain cock I touch leaks
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You should consider fitting drain offs on all down stairs rads. Draining where you suggest at boiler ,is unlikely to drain all downstairs rads.
you can get lockshield valves which have an integral drain-off.

The idea is neat, but the ones I've seen are rather poor quality.
The radiator drain cocks are an option. All downstairs radiators are actually above the level of the return / flow pipes at the boiler. If I drain at the radiators, would I still have pipework below that is still full of water. Its the pipework I want to make modifications to
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Just to add that first floor of house is approx. 2ft above the level of the garage floor
Ah ,ok. Then accessible drain cocks on the lowest points would be your best bet.
Thks, so better on flow or return ?, and would a gate / lever valve be ok instead of the Drain
Gate valves are pure junk . fit drain cocks to both flow and return ,thats what they are for.
Ok then, drain cocks on both. Is there a make or type of drain cock out there that wont leak at the screw ??? Like I mentioned before, Every one I touch seems to leak
Type B are slightly better than type A in my opinion . as they both have rubber seals ,they should be stripped before soldering onto pipework ,to prevent damaging the seals. After using them to drain out ,its wise to check the seals and fit new ones if need be ,before filling system up again. Nowt worse than filling up ,bleeding all rads ,then finding out the drain cocks dripping !!
You should consider fitting drain offs on all down stairs rads. Draining where you suggest at boiler ,is unlikely to drain all downstairs rads.
Ok then, drain cocks on both. Is there a make or type of drain cock out there that wont leak at the screw ??? Like I mentioned before, Every one I touch seems to leak

OP: Do your pipes rise from the floor to your radiators? I strongly suspect that they do, from your posts so far. if that IS the case, then you do not need DC's on each rad. I am a little surprised at TP's responses, TBH. He should know that ALL DC's are rubbish, and are probably the worst designed bit of heating kit. Hence your problem with the one on the boiler.

I would guess that the underfloor draincock has a "trap" in the boards immediately above it, although you may now have carpets or other floor covering above it. if you CAN gain access to that board, it will be worth looking. On the assumption that the pies are rising to the rads, and you can get access to that DC, my advice would be the following: Drain from the underfloor DC. When fully drained: If the DC is fitted on the end of a pipe, cut the pipe, use a socket, and extend the pipe, (do not solder yet) and run it through the hole currently occupied by a hose pipe. Use a socket and a new DC. Mark the pipe, so that when finally fitted, the drain cock spigot and socket sits in the wall, so the only thing outside is the body of the DC. Push the assembly out of the wall, and blow the socket and DC. Refit the pipe into the underfloor pipe, and solder. Now you can drain the system easily from outside, where drips etc won't matter. If the current DC is into a Tee, you will have to desolder the DC, or mess about a bit more with the pipework.

In my home, I have 2 Lever valves in a cupboard, with the outlets connected to pipes that extend through the wall to outside. To drain, I open the valves, and off we go. The idea can be varied endlessly depending on the actual situation.

When I did heating, for example,I always fitted a lever valve or ballofix to the cylinder feed pipework (obviously at the lowest point). To drain, one then just needs a hosepipe with a short copper pipe and a nut 'n olive. In case an imagination challenged individual worked on it after me, I fitted a DC into the outlet of the valve. To drain, remove DC, connect hose to ballofix, open and quickly drain away. Probably the majority of cylinder drain points are fitted in a totally inaccessible position, even of the DC opens properly.
Interesting observations FiremanT. After stating that drain cocks are rubbish and possibly the worst designed piece of c/h kit , you then go on to advise to fit one . you quoted my post re drain offs on all d/ stairs rads ,that was posted before the op told us the house was two foot higher than the garage / boiler location. Once he advised that ,you will see that i then posted again with different advice. With regard to your point that i should know that all dcs are rubbish ,i disagree. They are simplistic in design and the only thing that goes wrong / fails are the rubber seals. I cant begin to even take a wild guess as to how many drain cocks i have opened / closed / fitted in my lifetime ,but the amount that have actually caused me any problem could be counted on one hand. And from memory they were fitted badly ,in ridiculous positions on cold water feeds to hot water cylinders , so i am totally with you on your idea regarding taking them out the equation in that set up. And finally ...the gate valve is in my opinion THE worst valve ever invented !!
Regards Terry
Hi again FT & TP.
Thanks for your input. FT, you are quite right. there is a hatch cut into the floor above the end of system drain cock. Didn't know it was there cos of the under floor insulation ( Glass wool )and couldn't see it from underneath. I've got the system cleaner in now and will use this drain point for the initial drain, but it means pulling away some of this insulation and refitting again, plus there's woven material holding the insulation up. Once done, I think I'll take both your advice concerning Valves. I still like the idea of being able to drain from my garage. There's a drain pipe from Gutter right outside the door. I'll fit Tee's into the flow and returns in the garage, and fit lever Valves (15mm Peglar PB300 lever ball valves, as from what I can make out these are ok for CH systems ) and then drain cocks just after the Valves to give double isolation. If the drain cocks give problems I can just take them off and replace

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