Draining down/refilling a combi boiler system.

SaveSomeMore_2

I'm planning on draining down the central heating system to put a cleaner in (as lots of air in system/uneven heated radiators - house was ill-maintained so I doubt there is any inhibitor in), and again with an inhibitor a month later.

I've read a lot of websites and got a general jist of the process but I have some questions that sites seem to give conflicting info on:

1. When I'm draining down what needs to be turned off - is it the stop-c**k (loving the censoring! :P) and mains power to the boiler? Or does the boiler circuit need to be isolated fully? Is there an order for this?

2. To refill, do I turn the water on at the stop-c**k and re-pressurise the boiler using the key as when topping the pressure up? is this the right order and/or are there additional steps? (Some sites mention the boiler's filling loop - is this the simply the key business?)

3. Does the boiler need to be switched off (or isolated) still when re-pressurising?

Owain_Moneysaver

Keep boiler switched off at the timeswitch/programmer so it does not operate but if you have a digital pressure display you will need to leave the boiler power on so you can see the pressure.

The boiler circuit should be completely separate from other water supplies in the house so you don't need to turn off the main stop-tap or anything else.

The link between the mains water and the boiler circuit is the filling loop/key and that's only opened when repressurising.

If your system is really dirty you might want to fit a filter to the boiler return side so all the released muck in the system doesn't run into the boiler.

Be aware that mucky boiler water will stain carpets etc indelibly.

Mr.Generous

If its really mucky the downstairs rads will be worse, it might be worth removing them and flushing outside with a hose. If some are blocked you might have to turn various rad valves off to boost the pressure to blocked rads. It's not unusual with a sludge up system for it to get worse after the first flush, you may find so such muck shifted something else stops working.
Ive done systems where you need to close feed valve to an individual rad and let system back fill to dislodge sludge, you can flush over and over and still get crud out. Advice above is spot on too, and it sounds like you have done your research. All heating chemicals are reasonable at Toolstation ...
http://www.toolstation.com/shop/p94504?searchstr=inh

I don't work for them or anything, Screwfix probably just as cheap. Plumbers merchants will probably charge you more if they don't think you are trade customer, had it done to me when in a place don't usually go to.

SaveSomeMore_2

Thank's guys.

Owain_Moneysaver wrote: »

The boiler circuit should be completely separate from other water supplies in the house so you don't need to turn off the main stop-tap or anything else.

The link between the mains water and the boiler circuit is the filling loop/key and that's only opened when repressurising.

Ah, I see, so when you top up the boiler pressure that is just adding more water into the system? The more you know!

Owain_Moneysaver wrote: »

If your system is really dirty you might want to fit a filter to the boiler return side so all the released muck in the system doesn't run into the boiler.

A bit technical for me - it's quite cramped under the boiler so I think that would call for a plumber to move all the pipes round.

Fingers crossed it isn't too dirty, and hopefully the cleaner in the system will keep any sludge loose enough?

Owain_Moneysaver wrote: »

Be aware that mucky boiler water will stain carpets etc indelibly.

I don't think it is "too" bad - I had a small leak (loose valve) that was fixed and the water is a little off coloured (pale lager!) but not black.

If I put loads of towels/trays down and carefully bleed the air from top to bottom, and then close the vents before refilling I should be alright?

Mr.Generous wrote: »

If its really mucky the downstairs rads will be worse, it might be worth removing them and flushing outside with a hose. If some are blocked you might have to turn various rad valves off to boost the pressure to blocked rads. It's not unusual with a sludge up system for it to get worse after the first flush, you may find so such muck shifted something else stops working.

Removing them is a little bit above my ability and motivation levels I'm afraid!

I'll try isolating each radiator a bit before draining down to loosen things up.

Mr.Generous wrote: »

Ive done systems where you need to close feed valve to an individual rad and let system back fill to dislodge sludge, you can flush over and over and still get crud out. Advice above is spot on too, and it sounds like you have doIne your research.

I think I'll do a couple of drain and refills before adding the cleaner (and again before the inhibitor) to be sure.

I'm using Sentinel X400 cleaner and X100 inhibitor which I've heard is alright stuff? I'm guessing cheaper versions would have worked but hey ho!

I'm not really having any major problems with the radiators right now (just noise), it is more a preventative action as it probably hasn't been cleaned in a while (probably since installation), and hopefully everything will be a little more efficient and cheaper to run for the next few years.

Mr.Generous

If water in the system was a pale yellow colour it is ideal, sludge is black an if really bad slime comes out. Clear means no inhibitor so it sounds good to me.