Draining down a central heating system

[dannynolan]

We have three radiators on our CH system which remain cold. They all have TRVs, two of the radiators heat up when the valves are tapped. The third doesn't heat up at all. The system is heated by a Worcester Bosch Greenstar 30 CDI.

Before we replace the valves we want to put Fernox 3 in to see if that solves the problem.

We opened all the bleed valves and drained down the system. The F&E tank was very slow to drain, and probably didn't drain fully. Also a couple of (working) radiators stayed filled with water once everything else had drained.

1. Why might the radiators not be draining properly and how do we get them to drain properly?

2. The water coming out of the system is very clean. So is there any point in putting Fernox 3 in - given the number of double radiators we have we would be putting 1.5 litres in so not cheap. Though when we bled some of the radiatorss blacker water came out so might there be local corrosion stopping the radiators working that Fernox would clear out?

Thanks in advance

 

[RigidRaider]

Fernox won't clear out blocked rads, it's just a soap that makes the water alkaline so that it doesn't oxidise the insides of steel rads. Sounds like you need to remove the rads, take them outside and flush them with a hose.

What happens when you unscrew and remove the TRVs from the rad valves? They should be fully open then.

 

[Nige F]

1. Why might the radiators not be draining properly and how do we get them to drain properly?



Thanks in advance

The bleed valve hole might be blocked - remove screw and poke hole with a pin. As to the fernox , I'll leave that to more opinions.

 

[ianmcd]

There are no chemicals that clear blockages, all chemicals and powerflushing needs partial flow to improve systems performance, ALL blockages need to be physically cleared then you add chemicals

 

[dannynolan]

Many thanks for all the replies, much appreciated as ever.

According to the Fernox website Fernox 3 cleaner "removes sludge, scale and debris" so the plan was to run the system with the cleaner in it for a week, drain down again and refill with an inhibitor added.
If the cleaner did not cure the problem of the sticking TRVs we would replace the valves before refilling with the inhibitor added.

 

[dannynolan]

The bleed valve hole might be blocked - remove screw and poke hole with a pin..

Thanks for that, but not sure what you mean by a blocked hole as a continuous stream of water comes out when the valve is bled.

 

[Nige F]

That's OK then

 

[ianmcd]

Many thanks for all the replies, much appreciated as ever.

According to the Fernox website Fernox 3 cleaner "removes sludge, scale and debris" so the plan was to run the system with the cleaner in it for a week, drain down again and refill with an inhibitor added.
If the cleaner did not cure the problem of the sticking TRVs we would replace the valves before refilling with the inhibitor added.

AGAIN it will not clear any blockages, you have to get some sort of circulation in order for the chemicals to start working

 

[RigidRaider]

Close the valves at both ends of the rads, loosen the fittings, open the bleed, drain the water, then close the bleed and lift the rad off its bracket and swing it forwards until it's lying on the floor. Disconnect the rad and carry it outdoors upside-down so the black sludge doesn't pour out all over the floor. Then flush with a hose.

 

[dannynolan]

AGAIN it will not clear any blockages, you have to get some sort of circulation in order for the chemicals to start working

Ok sorry for being thick but where do you think the blockage might be and what do you suggest to clear it.

 

[ianmcd]

Could just be the TRVs sticking , remove the sensor heads and manually move the pin on the valve up and down and see if that helps, another thing to try is close down all the rads that are working and see if that forces the heat to the ones that are not working

 

[dannynolan]

Thanks for all your answers.

Have decided to replace TRVs, and would like your thoughts on the following :

When we drained the system the water from the hose was clear. When we bled the radiators (after refilling) the water from the bleed valves on some radiators (not all of them) was black. The Magnaclean filter was also very dirty (probably last cleaned about 15 months ago).

Would you suggest running a cleaner through the system for say a week. We have 14 double and 2 single radiators so would need 3 bottles of cleaner - would it be worth the expense and hassle ?

Thanks.

 

[terryplumb]

If you get all rads working ,then consider adding chemicals. Whilst some radiators are not working it'd be pointless.

 

[dannynolan]

If you get all rads working ,then consider adding chemicals. Whilst some radiators are not working it'd be pointless.

Got you, thanks for that.