Diagnosis of a central heating problem......

[NickyW]

Hi

We've got gas central heating insurance and had an engineer visit today as we thought the pump had stopped working. However, he diagnosed a 'dry system' and showed me that there was no water in the upstairs radiators. He said that the dry system was caused by a blockage and that we needed a power flush (I almost fainted when he said £300+)! However, after he'd gone, I switched the pump on just to give it a try and there is now water circulating around the system. Could it be that the blockage cleared, or might there be another reason for the problems that we had? I guess we need to get someone to come and look at it but I don't want to spend hundreds of pounds if we don't really need to,

Thanks in advance, Nicky

 

[gas4you]

From your description I would think that as you have a 'dry' system as he put it, the blockage will be in the cold feed from the F&E tank in the loft, where it tees into the heating pipe work. This needs to be cut out an replaced.

It is advised that you should have a powerflush after completing this, but quite often customers have the blockage removed and never get any more trouble for several years.

£300 is a bit cheap for a powerflush and I doubt that this would remove the cold feed blockage anyway.

The fact that you appear to have SOME water in the system is because the system wouldn't have been completely empty, just the high points. Also if it is a partial blockage water could have been seeping through it over time.

 

[NickyW]

Hi Dave

Thanks for this - there is now water in all of the upstairs radiators where there was none before but the pump is red hot. Could it be a problem with the pump??

 

[JohnD]

there is a chance that the blockage is not yet complete and there is a little water getting past it.

In that case you could use a cleaning chemical such as Sentinel X400
http://www.sentinel-solutions.net/en/heating/X400

it does not work in a completely blocked system because the chemical cannot circulate towards and through the blockage.

but it is only about £15 so worth a try.

If the water is not flowing freely down from your F&E pipe you might do best to drain some water out of an upstairs radiator and introduce it through the bleed vent hole (you need the Concentrated chemical in a tube for that). If you just tip the chemical into the F&E it will do no good unless it is washed down into the circulating water.

I would strongly advise fitting a Magnaclean as well. It will capture and trap the sediment which is already circulating in the water, and also all that is loosened by the chemical before it can collect anywhere else. It will cost you about £100 and is fairly easy to fit. It will continue working indefinitely and you can open it to remove accumulated sediment from time to time.

edit: If your pump is really hot then water is not circulating through it.

You might be able to fill up the system temporarily by putting a hose on the drain cock and connecting it to a garden tap.

 

[gas4you]

The pump shouldn't be red hot, but this could be a symtom of lack of water still.

Undo the silver screw in the center of the pump and see if you get water out. Whilst this is off put a flat bladed screwdriver in and see if you can rotate the pump.

(put a towel under the pump first as some water will run out and from the sounds of it it could well be very black or rusty )

I still think you have some sort of blockage in the cold feed as I posted before. It is very common.

 

[NickyW]

Hi

Water does come out when you open the screw at the front - when the engineer came this afternoon he put a screwdriver inside and the pump was turning.

I've been told to switch the pump off in case it catches fire - that's scary!

So, does it definately sound like a blockage?? Is it something we can do ourselves or does it need a plumber??

Thanks for all your help & advice

 

[gas4you]

Unfortunately I do not know your DIY plumbing capabilities, but yes a reasonably competent person could do it.

You will need to drain down the top floor first.

I would think that the pump has had it as well if it is really hot to touch.

 

[JohnD]

yes it does sound like a blockage.

there are two things you can do

try the cleaning chemical like I said

or

Take a magnet to the copper pipes where the 15mm Feed and Expansion pipe comes down from the loft, and joins in a Tee with the larger circulating pipes. the blockage is almost certain to be there and the magnet will stick to the copper pipe where there is a blockage inside it (the black sediment is iron based). you have to cut out the blocked pipes and replace with new. If you have compression joints you may be able to undo them and poke the blockage out with a stiff wire.

You must then clean all the sediment away using a chemical like I said or it will cause further trouble, and preferably use a magnaclean like I said.

As you are going to have to use a chemical and preferably a magnaclean whatever you do, you might as well get started. Use a hosepipe on the drain cock like I said to get the system full until water comes out of the vent pipe and the overflow.

 

[JohnD]

p.s. you and the engineer did look in the feed and expansion tank in the loft, didn't you, to make sure it has water in it?

 

[NickyW]

The tank looks to about 2/3 to 3/4 full. Is that as it should be?

 

[gas4you]

Yes