NR: Fitting radiators / Water top up.

[Gazz]

This may come across as a stupid question but I have no prior experience in this field.

I've basically bought a new radiator for our bedroom. We live in an old house and in 2 of the rooms the radiators are the single no convex type which I am led to believe are shit. So I've bought a double/double type.

I am considering fitting this myself but I'm a little confused with how the system works.

After doing a little research it looks like you just turn the water off to said radiator at both ends of it and simply remove and refit, but apparently there is a little water than comes out (usually dirty water). What I don't understand is where I fill up the water again to replace the water which will leak out. Is there somewhere like an expansion tank in a car in my house somewhere? That I need to top up to a certain level again after fitting the new radiator?

[doggone]

There will be a small header tank and it will probably top itself up from the mains, however if it's some kind of modern pressurised system I'm clueless.

[reckless_b]

Do you have a gas combined boiler,if so you refill the system via a link hose there
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[Skudd]

With old systems ( I'm purely an amateur but have done it myself) the easy way is to turn the two valves off either side of the radiator. The undo the bleed screw, the radiator then should be able to be lifted off the wall brackets, lean the radiator so that the bottom is still connected and the radiator water can come out of the bleed valve into a bucket or washing bowl, shallow and low is the bast to get all the water out. Then once empty remove from the bottom joints. Replace the radiator with the new one. To fill the radiator once in place open the valves at the bottom and gradually open the bleed valve letting all the air out until a small amount of water comes out. You may have to belled it a few times and the other radiators too, just to get all the air out.

It worked for me and I learnt by watching a plumber do it that way and it worked just fine for many years afterwards.
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[Andy_Pagin]

From memory - and no responsibility accepted if it goes horribly wrong!

Assuming a modern combi system.

Switch off/unplug the boiler.
Somewhere downstairs there will be a drain tap, usually on the hall radiator pipe. Stick a hose on it and poke outside the front door.
Close all the valves on the radiators you are not draining.
Open the drain tap.
Open the air vent on the radiator you are changing.
Let the system drain till nothing, or just a trickle come out of the hose.
Close the drain tap.
Close both taps on the radiator to be removed.
Stick a bowl under one of the radiator pipes and carefully unscrew it.
The water will be filthy, so take care.
Do the same the other end.
remove radiator.
Fit new one using ptfe tape.
Open both valves.
Under the comb there is a filler valve which may or may not have a pipe connected to a mains inlet (plumbers are supposed to remove it but often don't). Assuming the pipe's connected open the filler valve, switch on the boiler, let the gauge get up to just over 2 Bar, close the filler valve.
Go upstairs and open the air vent on the new radiator, air hisses out as it fills, close the vent as soon as water dribbles through.
Open the valves on the other radiators.
Back to the boiler, fill once again to get back to 2Bar.

Job done.
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[Gazz]

There is nothing modern about my house and I am assuming that the boiler is old as well. It sits in the loft and is a big cylindrical tank about 7ft tall . We only have a coal fire which heats the house. The tank looks like a sealed until that's why I was confused as to how the water gets inside it.

I originally thought that it came in from the mains water, but had my doubts since in the videos I have watched online about fitting new radiators - all the water is a rusty brown colour (and if it came from the mains, wouldn't the water flush out the radiator water and make it clear)? So that led me to thinking that it was a sealed unit and would need topped up somewhere.

[iooi]

[Robby]

It's always a sealed(ish) system - the same water is pumped round and round for years. Very similar in operation to the cooling system on an engine.

If the system is old and you're fitting a couple of new radiators, I would drain the whole system down and refill with fresh water and inhibitor. You'll need to turn the boiler off to stop it trying to turn on while there's no water in the system, and the boiler may also have some kind of automated filler (unlikely) which would need to be turned off.

Refilling is a case of finding out where the filling tap is - usually a normal water feed going into the boiler with some kind of tap on it - and turning it on until the system is full. With a combi you get a pressure gauge to tell you when to stop filling. You will then need to bleed all the rads, top up with water again, and then turn it back on.

Protip for a pikey powerflush, certainly works on a combi system. Get a hosepipe on the drain screw and point the hose into a drain, open the screw and let it drain a bit, then turn the filler on. Flushes the system at mains pressure, tends to push out a surprising amount of crap.

[Al]

If the system has a small header tank it will self fill, you just need to open the radiator valves when the new one is fitted and vent any air out of the radiator.
It will be the same process to fill a sealed system although rather then the header tank refilling the water that has been taken out of the system, you will need to manually open a filling valve, normally on or around the boiler or sometimes in an airing cupboard to top up the lost pressure.

That is assuming that the radiator is an identical size and a straight swap as well as both radiator valves not being seized, if so you will need to drain the system down or at least get a vacuum to work on the pipework.
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[MCN]

If you are fitting a new rad then you may as well flush the system before you fit it.
It only takes an hour to drain and fill with fresh water and put a cleaner in.

If it's a header tanked system simply turn off your cold water at your mains. This prevent the header tank filling via it's ball cock.
Locate the drain cock/s and attach a garden hose to the drain cock spigots.
Open the heating system drain cock/s 1/4" spanner or a wee shifter.
Open the drain cock/s and let the system drain.
If the water is black then you have no inhibitor which is bad as it means the water will be eating the radiators and the boiler.
The sediments produced by this action settles out and can restrict water flow, reducing heating effect and mean the boiler has to work harder to get heat into the house.
Fit your new radiator.
Close the cock/s.
Add a system cleaner.
Open the mains and let the system fill.
When it's full bleed the air out the radiators.
There may be a bleeder above the boiler to open too depending on the layout/plumbing.
Start the system and let it warm up.
Check your connections on the new rad for leaks.
Let the cleaner 'work' in the system for and hour or more or a few days and then drain it down again as before.
Fill and bleed and run for about an hour then drain and fill again.
The water will still be black/grey/dirty for a couple of flushes.
When you see the water is clear.
Close the cocks.
Add inhibitor and fill and bleed.
Run the system to circulate the inhibitor.
You can add boiler silencer too which helps prevent the boiler 'creaking' due to steam bubbles.
It is a good time to upgrade the bleeder to automatic ones while the system is drained.
A clean system will work better and using less fuel to heat the water will help pay for the additives.
I only use Fernox products and it costs about £50 to flush and treat an average sized system. Chemicals

If you have a pressurised system you will need to buy a 'filling loop' if there is not one already fitted.
This allows you to connect main water pressure to the heating system accumulator to fill and 'pre-charge' the system to about 1-1/2 bar.
The connection to mains must be removed to prevent the system polluting the mains when not being used to fill.

You can buy a piece of braided hose with crimped connections from B&Q for a few £s.
Buy a new drain cocks before opening the system.
The rubber seats can harden and will fail when opened.
You can sometimes escape by just replacing the core/stem from the new cock rather then having to replace the whole McGubbens.
That may be easier if your cock is soldered to the system.

This job is a summer time job.

There are companies who sell this service but the better job is when they attach a power flusher to the system (external high volume pump) and even bettererer some of them attach a vibrator and vibrate the radiators while the flushing pump hammers water around. They use a magnetic filter to hold the iron deposits whilst circulating which saves water and lets the client go Whaao... when they open the filter and show you all the iron stuck to it.
£400-£500 or more per average hoose
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Tarmacsurfer]

It'll be piped up something like THIS.

Backboiler systems are never sealed, they have to be able to vent in case of overpressure. There will be two, possibly three tanks in the loft, an indirect cylinder that stores hot water (there will likely be four pipes running into in, a feed off the stove into the side around mid way up that goes into a copper coil, a cold water feed into the side near the bottom and then a pipe at the top which carries hot water out to your taps).

There will also be a smaller header tank with an open top for the radiators that has a ballcock fitted, it'll refill itself as necessary from the main feed.

If you have a private supply such as a spring (like our place) then you'll definitely have a third large tank, open topped and containing cold for the system. Even if you're on a mains feed then you'll likely have one anyway as a feed for the header and hot water cylinder.

Two points, there's no guarantee there will be a drain point - I've seen many systems that were put together without for whatever reason. Christ only knows what the builder was thinking. And as others have said, it's probably worth flushing the system and refreshing the inhibitor. Check over your pump at the same time.

Edited for clarity - Two tanks, one cylinder. Not three tanks. One header for hot water cylinder, one header for heating, one heating cylinder.
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[mentalboy]

As it's not been mentioned, I was taught that you should bleed your rads in order, ground floor (or basement if you're really posh) first, top floor last.
For some reason not known to me, my mentor also preferred to bleed rads closest to the pump output first - but not overruling the flooring rule just mentioned.

[MCN]

And..... As Tarmacsufer suggests, hoi the pump off and clean out the impeller.
If the system has been neglected/minimal maintenance (as most are and folk worry about boiler maintenance insurance ) you can find little bits of detritus get caught in the vanes of the impeller. This builds up until it blocks the flow of water through the vane which causes a hydraulic imbalance in the pump and the pump will vibrate like a bastirt. You should not be able to hear the heating when it is running.
If you can hear water gushing through the rads it may nee the 'lock shield' valve adjusted slightly.
But that is another adventure. Balancing the flow.

A bit like Bandit carbs. Can be a skoosh case if everything is working but a beeatch if a valve is bad.
But a very therapeutic exercise and when balanced your system will sing (but into it's self, so you cannot hear it.)
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.