Half of my radiators are cold! Suspect sludge.. advice please!

[Andrew J C]

Hi

I live in a 2bed first floor flat with 8 rads, I have a 5yr old Vailant Combi boiler. The radiators in my kitchen, spare bedroom & storage cupboard are stone cold and recently the radiator in the bathroom cooled and stopped working. I've not had an urgent need to rectify this until recently.. the main issue is the spare bedroom which we would like to use as a nursery for a new arrival.

After doing some research I've re-blead my rads and also tried isolating the cold radiators but they still don't warm up. What I don't understand is there's water pressure going round the pipes so what is stopping the hot water getting through? If it's blocked with sludge and build-up in the pipes how does any water pressure get to the end rads?

I had a plumber come out and he's recommending a power flush, heat exchanger replacement or new boiler and new radiators!! That's a cool 3.5k I can't afford right now! Is there anything else worth trying? In the meantime he put in F3 fernox to work through for the next two weeks before returning to remove this and use F1 with mains pressure. What we have noticed is after a week the radiator in the bathroom has started to warm up again..

Any advice is very welcome..

I've told the plumber in question I can't afford the full replacement of my central heating system, he's now recommending fitting a magna filter (makes sense) but also a full strip down service of the boiler.

Thanks in advance

 

[terryplumb]

Do you have thermostatic rad valves ? If so ,did plumber remove the sensing heads to check pins are not stuck ? For a radiator to heat ,hot water has to flow into it from one pipe / through it and out ,returning to the boiler via the other pipe. So if one valve is off ,the water will fill the radiator from the other pipe ,so you bleed it and get water out the bleed valve.but it won't heat up. Hope this helps.

 

[Andrew J C]

Hi, no I don't. They're simple locking valves.

 

[Lower]

Swapping the radiators themselves without changing the boiler would be a much cheaper option.

It isn't a hard job to take a rad off to see if it is sludged up.

 

[terryplumb]

More likely the pipework is full of sludge on return ,or flow ,but not both. Is the pipework microbore ?? 10 mm diameter or less ??

 

[Andrew J C]

Thanks for your replies. The pipework is copper and it looks like its 10 mm in diameter.

The plumber said he was 85% sure the blockage was in the heat exchanger and or return pipework. I wanted to sanity check this (heat exchanger idea) as I've read elsewhere that a blockage int the heat exchanger usually results is unpredictable hot and cold water from taps and loud noises?.. we have constant hot water and the boiler is not making any loud noises.

Forgive my lack of knowledge but does the return consist of one pipe coming from the final radiator on the circuit to the boiler? Or is this from each radiator going back to the boiler?

Could it be a combination of some sludge in each radiator and pipework slowing down the hot water flow throughout the circuit? Meaning that the hot water cools down before it can get all the way through? It would be good to understand the workings.. sounds like I should take off each non-working radiator in turn and try and clean out myself if I want a cheaper solution?

 

[SFK]

Andrew,
Here is a good picture that shows (a typical) layout of pipes to your radiators.
http://wiki.diyfaq.org.uk/index.php/Central_heating_design

Basically one hot pipe goes to all radiators and one cold pipe comes back from all radiators.

Each of the radiators is then balanced (with their valves) so there is the same flow of hot water through them. (ie in that diagram the Radiators closest to the Boiler will have their Valves slightly more closed than the radiators further away from the boiler.


Did anyone check both locking valves (on each side of the radiators) to check that they are not stuck only slightly open (which might allow enough water through for you to bleed the radiator, but not enough heat it).


SFK

 

[terryplumb]

Your boiler has two large pipes ,22 mm diameter ,connected to your rads. One is the flow ,and hot water generated in the boiler flows out the boiler thru this and comes back via the other pipe ,which is the return. Every radiator has a branch pipe coming in ,flow ,and one going out ,the return. And in turn are connected to the respective flow and returns of the boiler. One way of doing this was to use manifolds ,basically a junction box. The manifold had 22mm flow from boiler and multiple 10 mm
Pipes going to rads.And exactly the same set up on return side. This is not the only way to plumb a system with microbore as each 10 mm can be branched off the main 22 mm flow and return. With regard to heat exchangers ,the plate heat exchanger heats the domestic hot water that comes out your hot taps ,and if it gets blocked you get hot / cold/ hot / cold water at taps, and does not supply hot water to your radiator circuit. It is the PRIMARY heat exchanger that does this.
As microbore Internal diameter is so small its much easier to block up with system crud ,and if you do have manifolds they are a prime culprit as some pipes block ,affecting some rads ,and others still function OK ,as not all the manifolds outlets are obstructed.