'Sealed' CH systems?

Brian Reay formulated the question :

It is pretty much the same process as a none sealed system, except you fill and top up, via a fill pipe. Get the pressure up to around 1bar, bleed, refill, bleed refill, until all of the air is out of the system and the correct pressure showing on the gauge.

So how do you 'get the pressure up', please?

usually there are valves under the boiler to refill.

NT

The guage should be on the boiler itself. Ours has to be filled to 1.5 bar. Below it is usually a filling loop - ours is a piece of flex hose with a t ap on each end (not sure why 2 as precious house had 1). These connect the incoming mains to the sealed system so open the tap(s) until the guage reac hes the desired pressure.

See the DIY Wiki

• an expansion vessel about the size of a football
• a filling loop
• a pressure gauge
• a pressure relief valve which spills water through a wall to the outside world in the event of the pressure rising excessively

With regards to capping the pipes under the floor, if you do one pipe at a time there won't be all that much water spillage. Clean the pipe with wire wool a couple of centimeters either side of where it is to be cut, (if it's upstairs where spillage matters) put a foil food dish under the cut location to catch the spillage, cut the pipe cleanly with a pipeslice, and have a copper pushfit endstop ready to shove on.

And have a wet and dry vacuum cleaner to hand (in wet mode) for when whatever container you use is about to overflow.

Thank you everyone who has responded.

I will be visiting her later this week and will try to determine if it is a sealed system and look at the pipes- so far I've only seen photos and those weren't in context (ie what exactly is underneath/around etc).

Keep in mind that there are some boilers (some WB combi models for example) that have the filling loop built in - you need to use a key supplied with the boiler to get it to fill.

On other like many Vaillant ones the pressure gauge is electronic and shown as a bar graph style display on the boiler's LCD.

Sealed systems are actually more convenient to work on. Main reason being less prone to air locking when re-filling, and no pumping over problems. Meaning you can have pretty well any circulation speed you want. So generally much easier to bleed after doing work.

You'll have to find the filling point. The hose which goes between the filling point and the mains cold water supply may be missing - some remove it. And I've seen some installations where this hasn't been made easy. Other than that you can treat things much like an open vent type.

One thing is to try not to overpressurise it. There will be a pressure relief valve set at about 3.5 bar so nothing dangerous will happen. But once this valve has lifted, they sometimes never seat properly again, so you always have a slow leak and loss of pressure. Apart from being a PITA to have to keep topping up, every time you do so you introduce some dissolved oxygen and over a long enough period you will deplete the corrosion inhibitor. This is bad news (particularly with combis) because oxidation products block up their secondary heat exchanger, and you won't get good hot water flow.