Hot water not heating when central heating is off

[EdR]

I drained the system at the weekend to remove a radiator - all went smoothly.

I cleaned out the ch tank in the loft which was pretty dirty. Lots of black sludge. Also cleaned out the magnaclean which had more of the black sludge.

When I refilled the system it filled slower than I expected (took over an hour), but I bled the system from bottom to top and the CH and HW all worked. I have bled again over the week.

Now six days later the HW doesnt heat unless the CH is on.

Any advice?

 

[JohnD]

you say it is very dirty.

A chemical clean with X400 or X800 will do nothing but good.

 

[ALCPlumbing]

Sounds like some sludge from the tank has partially blocked the cold feed to the system.
The hot water not working independently of the heating is most likely down to the motorised valve.

 

[EdR]

Thank you both.

So it would seem that I should flush out the system (whether using chemicals or just water or powerflush).

Wait to see whether valve has become ungummed. Comment 1 suggests this might just fix it.

If not I need to look at the valve in more detail and decide which bits of it need replacement - whole valve/actuator/motor.

Is this a common problem, and if so is there a common effect (eg flush system, replace actuator)

 

[EdR]

Thank you. Combination of X400 treatment and removing the powerhead and loosening up the valve seems to have done the trick.

Final question. How long would you leave the x400 in place? The instructions say up to 4 weeks. I have no idea whether longer is better, or whether I should flush it out now that the job is apparently done, and treat with inhibitor.

 

[JohnD]

it will carry on working, and loosening the sediment, as long as it is circulating* so when you don't need heat, keep the pump running but turn the boiler stat down so it is still going through the radiators. If you keep emptying the system filter, you will see the amount of sediment dropping off as the system gets cleaner. You can turn off all rads except one for a while, to get a more forceful flow through that one; then do the same with the next.

Even after you have drained and rinsed it, and refilled, the extra disturbance will cause more particles to come loose and get trapped, which is great, if you have a filter. On final refill, add X100 to reduce future corrosion.

*after about four weeks, X400 loses its power and the particles start to re-deposit, so you must flush it out.

 

[EdR]

That makes sense. This morning I was "rewarded" with a magnaclean full of sludge. I will work my way round the radiators as you suggest until Magnas clean and bright

Thanks very much for your clear instructions.