Replacing Radiators before boiler replacement

savings37

Hi, I'm looking at replacing our central heating system from a conventional to combi.

Whilst the boiler is being changed I'm wanting to change the 70's radiators for new ones. I would like to change the rads myself before the boiler is changed. I've fitted my own bathroom etc before.

Does anybody know of any downfalls to carrying out this work, I'd imagine most of the sludge would be taken out of the system with the rad changes hence I'd be okay running the system back up to check for leaks etc. I don't want to pump sludge through the new rads unnecessarily. 

I'd be planning for the new combi to be fitted a week later.

will-he-payitoff

If you have the system flushed and a magnitec filter fitted you should not have any problems.

savings37

will-he-payitoff said:

If you have the system flushed and a magnitec filter fitted you should not have any problems.

I was hoping this to be the case. The flush and magnitec would be requested aswell. 

Now to tell the family that the heating and water will be off for a week 🤦‍♂️

FreeBear

savings37 said: Whilst the boiler is being changed I'm wanting to change the 70's radiators for new ones. I would like to change the rads myself before the boiler is changed.

A couple of points to watch out for - 1970s radiators are quite possibly old imperial sizes. Most modern ones will be metric (you can still get imperial at a price), so you will probably have to modify the pipework. Watch out for different pipe sizes 1/2" is close enough to 15mm not to make a difference, but if you have any 3/4", 22mm pipe fittings won't work - With compression fittings, use imperial olives, soldered fittings need to be imperial.

Do fit TRVs to the radiators - It will be a requirement for the boiler installation to be signed off. It is also worth oversizing the radiators by 25-50% to allow you to use lower flow temperatures (this gives you better boiler efficiency). With larger radiators, you will be in a better position to install a heat pump if/when the time comes - On that point, it may pay to look at the pipe runs and try to rationalise the plumbing - In a well insulated house with decent windows, there isn't really much need to shove the radiators under windows.

Oh, and get yourself some blanking plugs to seal the tails coming out of the old radiators. Even after draining the system down, there will be a fair bit of black icky water that will stain everything if it dribbles out. Plug the tails before lifting the old radiators off the walls and carrying them though the house.

TELLIT01

Our radiators are also imperial and, when I looked at replacements, the approximate equivalent metric was generally slightly shorter.  There are adaptors available to allow replacements without doing work on the pipework.  There is a limit to how big a difference they can bridge.

ThisIsWeird

As said above, Savings37. And, going by your moniker, you will be looking for some? 'Oversize' the new, certainly in the most used rooms.

As for the sludge, you will likely find that most will be in the old rads, so you'll be getting rid of that along with the actual rads. The remaining coating in the pipes will hopefully be shifted by the power/chemical clean that your system will be given.

This is more important with combi boilers as these have very narrow chambers inside them, especially in the P2P exchanger, and these are far more prone to being clogged up over time than other parts - as i know to my cost.

But, you are doing a 'good thing' in removing the rads.

Belenus

Now to tell the family that the heating and water will be off for a week.

Can you wait a few months until the weather is warmer or is the replacement boiler urgent?

savings37

All excellent tips thank you, yes I'll be fitting TRV's on all rads. 

I have measured for new rads and yes I'll have to go slightly shorter and use valve tail extensions.

I've been using an online room size calculator to calculate for the required rad BTU size. I'm also trying to not get rads that come away from the wall too far which will require further pipe work. It's a bit of a balancing act.

When oversizing rads do you mean fitting a 21 or 22 in place of an 11 type? 

savings37

Belenus said:

Now to tell the family that the heating and water will be off for a week.

Can you wait a few months until the weather is warmer or is the replacement boiler urgent?

Yes I can wait, I have some time off at the beginning of March though so it might be an opportunity then. 

I currently have a faulty 3 way diverter on my system, boiler is 20+ years old and a leaky trv on my lowest rad. Nothing critical, but putting everything together it's prob a good time to update.

FreeBear

savings37 said: I've been using an online room size calculator to calculate for the required rad but size. I'm also trying to not get rads that come away from the wall too far which will require further pipe work. It's a bit of a balancing act.

When oversizing rads do you mean fitting a 21 or 22 in place of an 11 type? 

Most of my vintage Type 10 (single panel, no fins) have been replaced with Type 21 - In my opinion, the best compromise on projection and size. Type 22 just sticks out way too far.

Where online calculators have indicated an output of 3000BTU, I've gone for 4500BTU. Picked up some 600mm x 1000mm Type 21 radiators for a good price.

Richard1212

According to a BBC article I've just been reading, you can throw away your radiators---the future is : 

Electrically heated wall paper