Radiators not heating

Hi, I am wondering can anyone help with this problem.
We are in a ground floor apartment, and 2 from 5 radiators will not heat up. I dont believe that the two rads are the first or last rads on the system. We had a leak about a year ago, got it fixed, then had radiators cleaned, the rads worked for a few weeks and now are faulty again.
We have had two plumbers in to look at it, and we have conflicting advise. One of them says there is a leak(s) somewhere and all the piping shouls be replaced. (the pipes are embedded in the concrete floors !!) The other says the rads and system just need to be cleaned (suggesting that they were not properly cleaned in the first place).
Can a leak or leaks prevent some radiators not working while the other rads are ok?
Any feedback will be appreciated.

It would have to be a massive leak to do that, try opening all of the lock shield valve to clear the system out and then slowing turn them to restrict the radiators nearest to the pump first, the furthers radiator should remain wide open

Thanks Roker for quick reply. We have not a clue what the lock shield valve is. Help!

The leak can be proven by organising a pressure test on the system. { update with care on a 40 year old system ]
How old is the apt?
Is the pipework you see copper plastic or steel?
However before doing that, can you describe the heating system a bit more: is it oil or gas and have you your own boiler?
How is the hot water heated?
do u have a hot water cylinder, do u have loads-a hot water
{ You have a hot water cylinder so the coil in it could be leaking as well)

What happens if you shut off all the working rads?
The lock shield valve is the one on the rad that is not used to adjust the on off.

The apartment is about 40 years old.
Pipework is copper
Gas central heating with own boiler
Water is heated through gas boiler
Plenty of hot water
Thank you. now I know what a lock shiel valve is.

okay, try turning off all the other rads

If all the kit is 40 years old then it could be stuffed with crap which is very difficult to move.
When u say cleaned, were they all taken off and flushed outside with a powerful flow of water or was is 'done' in situ
Update based on your next post
If the kit is 40 years old and has not had the proper anti corrosion stuff in it, then a full "deep clean" of the pipework and rads may cause pinholes in the steel radiators.

A pressure test may do the same as in many cases the steel has corroded to the paint, put the sludge and low pressure stops it leaking.\

Likewise with the pipes embedded in the concrete, it is possible that they are corroded as well.

Ditto with the boiler, there could be a leak in the heat exchanger which is tough to track as the flue gases are mostly steam anyway

For any cleaning of the system, the boiler needs to be taken off the circuit.

The rads were cleaned in situ. We have just discovered a leak underneath the tank in hot press. Not sure how big the leak is.

Have you tried opening the bleed valves at the tops in case they are air locked?

josoap;

Can you let posters know which area you are in; methinks you need to get a good recommended plumber.

Hi, Thanks all for replies to date. We have bled the rads on several occasions. Gerry, we are in Dublin 3.

josoap said:

Hi, Thanks all for replies to date. We have bled the rads on several occasions. Gerry, we are in Dublin 3.

Click to expand...

I have updated some of my earlier posts based on your replies so you might re-read them to make sure you understand the issues/risks.
If you are not clear, ask again.

Hi josoap You need a VERY good plumber, preferably one with knowledge of gas heating system

I had a similar situation and my very good plumber did everything obvious and unobvious to rectify the two stubborn rads.

The amount of filth in the rads was incredible having been thoroughly flushed outside. You need a man who WANTS to solve your problem .

Reminder, any posts seeking or providing recommendations should go in the Recommend tradesmen and suppliers forum.