Radiator heating dilema

[Meggalar]

I've just had Eon visit today under our maintenance contract to try to fix our central heating but its not worked...
The rads are only getting warm on the top and are just not heating the house so wife and kids not happy. I've already taken one rad off and flushed with a hose, there wasn't a lot of black sludge that came out so i'm thinking its not sludged up. Despite this the radiator hasn't improved.
So called Eon out.
They came out and said it was the pump and changed it. However its made no difference at all, so i'm at a loss what to do next.
They have recommended a powerflush but i'm not convinced and also we can't afford it. There are 15 rads in the house so would cost around £400!
The system is a vented cylinder indirect heating using an Ideal NF70 Boiler about 16 years old i think. There is an expansion tank in the loft.
Should I try some Sentinel X400?
Is it worth paying for the powerflush or is there an other option?
Any advice would be much appreciated.
Cheers

 

[Armo74]

If you have any TRV's remove the heads and make sure the pin's move up and down.

You could also have a go at balancing the system see FAQ's.

Check the pump setting.

 

[picasso]

Could also be the thermostat in the boiler , is your hot water as hot as it normally is ?

 

[Meggalar]

Thanks so far, there are no TRV's on our rads.
The boiler thermostat was replaced 2 years ago, i had suggested it was the same problem but because it was recently replaced they discounted that and went for the pump. I'll check the water temp.
Also the thermostat in the hall, at the moment its turned up high at 24 but its clicking on/off at about 14, i assume its ok just the room temp not very high. Should it be calling for heat all the time?
As i said i dont think the rads are sludged as ive cleaned a few, could it be the 8mm microbore inbetween?
All suggestions appreciated. Thanks

 

[Meggalar]

Pump setting is on 2 out of 3. On old pump it was always on one when it used to work properly.

 

[Agile]

If you have proper pump valves then remove the pump head and do the bucket test on each valve as sometines they can get blocked.

A thermal survey when the system is working will also often identify where the problem lies!

Tony

 

[Agile]

Its unlikely that most people doing power flushing will solve your problem unless you make it conditional on the job.

Many of those I hear of seem to be unable to understand that whats needed is to solve a problem and not to come and mess about for a few hours and charge £350.

Tony

 

[Meggalar]

Hi Tony,
What do you mean by a bucket test? The new pump is a Grundfos Selectric one I think. There are 2 x 2 way motorized valves near it, one on pipework to the hot water cylinder and the other on pipework to the boiler.
Many thanks

 

[Meggalar]

Over the weekend I put 2 bottles of Sentinel X400 in the central heating system, which appeared to do the trick and the rads were nice and hot again with the heating on most of the weekend.
Now its Monday evening and the heating is back on but its gone back to how it was when I first started this thread - warm but not enough to heat the house.
The water leaving the boiler is really nice and hot, its like this at the pump also but the radiators are no where near as hot as this. I've also noticed that the hot water from the taps doesn't appear to be as hot as normal. Its warm but you can hold your hand under it no problem.
Any ideas what to do next?
Thanks

 

[Hugh Jaleak]

If stat is clicking on/off at 14, then it seems that may be working ok, and the room is flippin cold... It still seems it may be a circulation problem, can you trace the pipe from the pump and see how far the heat is getting? It does sound like system is working eventually but taking a long time to get there.... Does boiler fire for short bursts now and again, rather than a continuous firing when initially switched on from cold?

Do you have an air seperator? (Small 'can' size part in the pipework before the pump. Should have 4 pipes connected to it, one from boiler, one to pump, vent from top and cold feed.) These are prone to blocking, see if a magnet will stick to that or any other area of pipework.

X400 wont work overnight, give it a week or 2 in an older system, but even then it wont clear a badly blocked pipe.

 

[Meggalar]

Thanks Hugh.
Boiler tends to fire up for about 3 minutes to start with and then comes on about every 5-10 minutes for about 1-2 minutes.
I can't find an air separator as you describe but I have taken a picture:

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• Meggalar
• 10 Dec 2012
• 1

Untitled

• Meggalar
• 10 Dec 2012
• 1

A previous engineer had used a magnet on pipework near (below to the right) the pump and said that it had some sediment in it, and suggested getting a local plumber to cut out the pipe section and replace. This was in response to me telling him that the radiator nearest the pump needed bleeding regularly. He also suggested that the build up of sediment could be causing it to vent to the F&E tank in the loft.
All the rads are acting the same way, so I don't think they are all sludged up and were working fine on the weekend, could it be a partial blockage on the microbore?
Would this also affect the hot water heating?
Many thanks!

 

[Hugh Jaleak]

No air seperator fitted with your setup, looks a rather odd layout of pipework, but seen worse! The microbore wont affect the HW, the pipe rises from the pump, tee splits flow to CH and HW, the top pipe continues to the motorised valve and then into the cylinder coil.

Symptoms suggest poor circulation, boiler heats the water but as its not getting away very quickly, the boiler stat shuts the boiler down. Heat slowly moves away from the boiler, temp drops and boiler fires again, cycle repeats, meanwhile system is slowly getting warm. You said heat is getting to the pump, how far is it getting past the pump? I cant see it being a blockage if the system was fine at weekend, blockages tend to stay there until physically removed! Pump may be new but it does beg the question is it doing anything?

 

[Meggalar]

Thanks Hugh.
The pump is brand new so im assuming its working fine and I guess it must have been working on the weekend for the rads to get nice and hot.
The more I think I about it I guess poor circulation sounds more likely, i'm just cautious about spending a small fortune on a power flush if its not going to cure the problem especially if it might be covered under the maintenance contract.
I thought the X400 might 'dislodge' sediment and potentially lead to a blockage, i've seen a few posts suggesting it can happen.
Cheers

 

[Hugh Jaleak]

If it was working fine and suddenly isnt working, to me that suggests a sudden failure, rather than a slow decline as would be expected with a system slowly sludging up. Pump provides all the circulation in this type of system, hence my suspicions about the pump. Never assume anything! Have you checked it is definately working? Could be something as simple as a wire not been fitted correctly when pump was replaced and has broken or come loose.

X400 will loosen sediment, but a blockage sufficient to stop circulation almost completely will build up over time, not overnight in my experience. Really cannot see a powerflush making any difference, the system did work ok at the weekend! (And I suspect you'll find in the small print, powerflushing isnt covered....)

You've not drained the system since adding the X400? I'd also check the air bleed on the leg of pipework above the pump. If that section is full of air it may struggle to work..... (Have a spare at the ready though beforehand in case it wont seal again. )

 

[Meggalar]

Thanks again Hugh.
I'll check the pump, though there does appear to be a small amount of hot water getting through but only enough to heat the top of the radiators.
I wondered about adding another bottle of X400 to see if that helps, bearing in mind there are 2 bottles in there already.
Also I wondered if there might be a partial blockage at microbore manifold, although I don't know where it might be, under the floorboards somewhere?
Thanks