Back boiler - bleeding the rads and water top-up

[Smithy]

Could someone please help me understand how I go about topping up the water level of a back boiler.

 

Where I recently moved in to, there is a back boiler which is both old and needing of replacement. Until that time comes, I need to bleed the rads, but I've even never seen a back boiler before.

 

With a combi-boiler the filling loop and pressure gauge are usually next to the boiler, would I be right in thinking that when I pull out the fireplace, the filling loop and pressure gauge will be visible next to the boiler? Do back boilers even have the ability to have the water topped up?

 

I haven't touched the thing yet until I get a better picture.

 

Many thanks, Smithy.

[PeterW]

There should be a copper or steel header tank in the attic with a feed and expansion pipe on it. Will automatically top the level up as you drain off. Worth chucking a couple of bottles of inhibitor in it too. 

[Nickfromwales]

Yup, the old systems use gravity to an open F&E ( Feed and Expansion ) tank at the highest point of the system, so this could be in an airing cupboard also BUT it could also be topped up from what is called a "Primatic" hot water cylinder, which is a regular looking copper cylinder but it has a bellow / diaphragm inside it which allows water to be forced into the central heating 'loop'. That force is generated by the much larger CWS ( Cold Water Storage ) tank in the attic but you MUST NOT ADD INHIBITOR if the system is primatic.

Locate the tank, or if no tank then check the type of cylinder and report back here ( with some pics if necessary ). If there are a pair of tanks, then the smaller will be the F&E, and you will need to check that this is full of water ( at least 1/3 to 1/2 full is norm but can be higher ) as sometimes the reason the rads need bleeding is that there is a blockage in the T where the F&E pipe connects to the system and that stops the system being automatically 'topped-up'. There is a lot to check before dabbling with an old system, so get clued up ( as you are doing here ) and then go at it. 

 

If all is good then bleed the rads one at a time, starting downstairs and work your way up ( if it's a 2-storey property ) so that will allow the system to regain its 'head' of pressure between bleed off's. Do this with the heating system switched off, but if you get no joy then try it again with the heating pump on and running with the rad valves all fully open. Beware, old rad valves do NOT like being opened and closed, and will likely leak a bit when you do so.

Happy days !

[Smithy]

This is fabulous, thank you both so much!

 

Yes there is a big black monstrosity up in the attic, right above the tank, which is in the cupboard in the main bedroom. If I recall correctly it was kind of wrapped in black plastic and I just left it alone.

 

I'll process your info and go check it out, and come back in a couple of days.

 

Many thanks, Smithy

[Smithy]

Hello again, to continue this subject, I've been back up in the loft, and taken some pics, also of the storage tank in the first floor bedroom, directly under the loft tanks.

 

There are two tanks in the loft, large to the left and smaller to the right.

 

So to come back to my original question, I want to bleed the rads, so does this mean that the overall water level is self-regulating and therefore self-filling?

 

I've included photos of the bedroom hot water cylinder, would anyone care to to guess whether that is a Primatic or not? As the system is old but still with some life left in it, we would be interested in helping it in any way we can.

On 11/08/2020 at 06:04, PeterW said:

Worth chucking a couple of bottles of inhibitor in it too. 

 

If the consensus is that it would be worthwhile adding inhibitor, what type would you use?

 

Many thanks again, Smithy.

Edited August 27, 2020 by Smithy

[PeterW]

The small tank is the header - the large is the main water tank for the house so don’t put anything in it ..!

 

Any inhibitor will do - Cura ones are fine and cheap