How do you drain down a central heating system on a combi boiler?

KingL

I have the chance to go away for the winter.

I don't want to waste money heating an empty flat, but equally, I don't want the pipes to freeze and flood out the downstairs neighbours when they thaw, so I thought I would drain the radiators and leave them empty (and open) while I'm away.

The CH system is on a combi boiler. I have googled for how to drain down radiators, but all the results seem wary of saying how to do it for a combi. Is it really so difficult/dangerous? How do you do it?

There are 3 ordinary wall mounted radiators at the same level and one heated towel rail at a slightly higher elevation. I'm not aware of any drain valve - so I was thinking I'd just undo the nuts where the copper pipes join the radiators and somehow capture the effluent. Is there any more to it than that?

Clearly, draining the rads at a point 10cm above the floor is going to leave water in the pipes below, but I'm thinking that if they are left open ended then expanding water has a way out? Also there are flats below, so they will get some rising heat.

When it comes to refilling, there is a tap that fills the CH circuit from the water main.

The boiler is a Pottertons combi 80 (rebranded "Puma", I hear). I've got the books for it somewhere.

Is threre anything I should know before taking this on?

ormus

you should have one of these somewhere. (lowest part of the system).
put a hose pipe on it, with one end outside, and just drain off the water.

robv_3

Don't bother draining it down for a couple of reasons....

o- As your in a flat its very unlikely the temperature will drop to freezing due to being heated from downstairs.
o- If the flat does freeze other things are going to be affected.
o- You will never get all the water out. It could still freeze.

Just turn your thermostat down to ~5 degrees and if your combi has internal stored hot water make sure its disabled.

mikey72

I would have agreed with that, and said leave the boiler on, stat at 5C, or on it's own frost stat, but last winter I know of several condensing boilers that had the flues freeze, and shutdown in fault mode and have to be manually reset, so maybe leaving it off the economy setting would help. I wouldn't empty either though, as I would also think the flat downstairs would keep it from freezing, unless lot of the pipework for yours runs through the loft space.

KingL

Thanks for the replies so far.

My main question is whether there are any specific procedures for draining a system attached to a combi boiler, (as opposed to an open one with a feed-expansion tank). Sites like this suggest it is a big deal

Draining and refilling sealed heating systems- Because the water in these is under pressure, and refilling is not as straightforward, you should seek the services of a professionally qualified plumber for this.

Sure it might not freeze, but then again it might. And I don't really want to leave it to chance.

Unfortunately, there is no ambient thermostat in the system (nor economy setting), just a TRV on each rad, so just leaving it on a low setting on the main thermostat isn't a runner, I'm afraid.

I don't think that I have a drain valve at the lowest point. And ripping up rooms of laminate flooring and/or floorboards in the hope of finding one is deeply unappealing.

If I have to leave the water in the pipes under the floorboards in situ, then so-be-it I suppose. I'd rather leak 5 litres of water, than 4 radiators full.

I'm now thinking that maybe I should drain say 20% of the water out, top it up with an antifreeze and run it for a day to mix it all in....

Suggestions welcome, but my main point is what are the special considerations for draining a system that is attached to a combi boiler

TIA

mikey72

From your user instructions


Additional Frost Precautions
There may be some pipework etc, that is vulnerable to frost and additional protection will be required. Various methods can be used:-
Page 10
1. Insulation of the boiler and pipework, taking care not to impede any ventilation or air supply.
2. Completely draining the water system if not in use for long periods. On a sealed system, draining and refilling must be carried out by a competent person.
Note: Although the system can be emptied by using the drain off taps installed in the pipework around the system, to empty the boiler, it is necessary to remove the drain plug under the pump manifold. This should only be done by a competent person.
3. Have an additional low limit thermostat fitted.
Note: Frost protection devices cannot operate if the boiler is completely shut down and the electricity supply turned off. Where there is vulnerable pipework and no additional protection is provided it may be necessary to run the boiler at the low setting at times when it would normally be turned off.

Do you have a room stat anywhere in the flat?

Or

http://www.sentinel-solutions.net/en/heating/X500/application

KingL

Thanks for this, that helps

Although I can't help wondering what it is that a "competent person" would do that an "incompetent person" couldn't.....

Do you have a room stat anywhere in the flat?

Nope.



I guess I will probably go the antifreeze route.


thanks for all inputs, much appreciated

bockster

not absolutely sure, but i think antifreeze is a no-no in heating/hot water systems.
in case eventuality, heatexchanger faults and allows water (+antifreeze) from primary side into secondry side which is the hot water out of your taps. this hot water could then be poisenous if consumed.
a little far fetched i know, maybe anyone else can advise?

i suppose the same could be said of inhibitor in the system, but maybe inhibitor is less harmful, i don't know.

hc25036

Trying to think laterally, maybe the cheapest/safest option in the long run could be to have a roomstat fitted. Shouldn't cost too much and solves all the problems of finding a "competent person" and the risk of freezing pipes....

Mojisola

KingL wrote: »

Unfortunately, there is no ambient thermostat in the system (nor economy setting), just a TRV on each rad, so just leaving it on a low setting on the main thermostat isn't a runner, I'm afraid.

Not an answer to your main question but I thought you had to have one radiator without a TRV in case they all closed off when the boiler was pumping.

roddydogs

You do-usually in the Bathroom.