Descaling a combi boiler

[Marnhullman]

Do I have to remove the heat exchanger on a combi boiler to descale it and if so how? If I don't have to remove it how do I get the descale liquid into the system?

Thanks

Mike Collard

 

[boilerbeasty]

Well you can put general cleaner in the system, which will pump through the heat exchanger, and should remove scale albeit slowly. You then have to drain and flush the system a few times.

Or you can drain down the boiler and remove the heat exchanger and put some directly in to it and leave it to descale (with DS30 or similar). Alternatively, you can hire a machine to pump descaler chemical back and forth through it, or take it to a local plumbing shop which offers the same service.

Or if its really badly scaled and old, and you can get one cheap, and you value your time just replace it with a new one.

 

[Marnhullman]

Boilerbeasty

Thanks - will consider all options.

Snowsride

 

[oilman]

Is it the primary or the secondary heat exchanger? If it's the one that supplies the hot water, you will have to remove it to descale the tap water side.

 

[COG]

If you have limescale you will have to connect a descaleing machine to the mains hot and cold domestic pipes to the boiler after first disconnecting it from the system,remember the lime scale will be inside the water pipes not inside the primary pipes, what boiler b describes will clean out a build up of sludge ect in the boiler,some small firms offer de scaling at there premises if you take your heat ex along but that involves a lot of work plus if you attach a machine on site it will also clean out the boiler water ways ,div valve, flow switch ect

 

[Marnhullman]

Descaling begins to sound like a bridge too far. Will consider repacing the heat exchanger.

Thanks to all contributors

Snowsride

 

[COG]

Try your local hire shop, see how much it is to hire a descaler then price your new water to water heat exchanger ,it only takes about 1 hour to descale a boiler if you have good access to the pipework comeing into the boiler.

 

[niftynigel]

I recently had this problem where the Heat exchange had clogged up with scale, serves me right for buying one in a hard water area. However I did and do have two water softeners/conditioners connected to the cold water feed. one electronic and one combimate chemical.

after searching though google for Diy descaling I found this thread, hence the reply to it today in the hope that I can inspire or help another person like myself.

In short your comments here gave me the thought to do this myself, first off, I had an old centeral heating pump in the garage and a pile of speedfit connectors and pipes, I disconnected the inlet and the outlet to the domestic hot water side of the heat exchange and then connected the pump in a loop configuration with an extra pipe for filling. I plugged the pump in and started to fill the system with kettle descaler, I bought it from my local hardware shop for £2.50, a 50/50 mix filled the system and I let it run for an hour.

this seems to have completely cleared the scale and we are now once again having hot powerful showers once again.

thanks again guys, Picture, albeit of my crude hash-up here

http://www.marvernhouse.co.uk/descale.jpg

 

[stevekane]

Well I have to say that this seems to me to be an excellent way of descaleing the heat exchanger, my son has an older combi boiler that works just fine but the flow of hot water is woefully slow, I guess its all scaled up, so Im going to try a DIY descale along the same lines as yourself, Can you tell me though, was there enough water presure to allow the boiler to fire up and heat the water or did you use the mix cold? I was thinking about useing say Washing Machine hoses to connect up to the boiler and I have one of those small drill powered pumps to circulate the de-scale mix, but I doubt it would be powerfull enough to fire up the boiler, perhaps I will use an electric kettle as a heater tank??, anyway many thanks for the tip and the photo, its got me thinking the problem through and Im sure its not going to be too difficult.
Steve.

 

[daveaf]

Forget the off the shelf chemicals, they are all ccrapp. I spent about £80 on all different products and they did nothing. In the end I took the heat exchanger out and took it work where i soaked it in a VERY strong (50%) sulphuric acid for a day. It completely stripped all the scale and now it is like new. If you do not have access to these chemicals, take it to a metal electro plating company where they will have a hydrochloric acid bath to soak it in.
My exchanger was made of copper so it was fine, but check with the company first.

As for power flushing People charge £400-£600 for this. You may as well buy a new boiler.

Kettle descaler is ok, but all these chemicals are phosphoric acid based and are very weak in comparison.
If you have the ability to remove it, then I advise you to, and do the above.

 

[honesteddie]

Just thought id share my recent experience in descaling my old Worcester combi boiler, the hot water was taking longer to heat and would overheat,what i did was to use an old pump and isolate were the cold water enters the boiler and pump descale solution into the boiler ,turn on the hot tap letting the water flow into a bucket , the hose for the inlet on the tempoary pump was in the bucket so just recirculating the solution ,to connect in to the boiler i used a isolating valve followed by a washing machine tee to connect the inlet hose (washing machine hose) from the pump.
This seemed to be the ideal solution without having to remove the heat exchanger, i have taken photos if interested !

 

[kevindgas]

As for power flushing People charge £400-£600 for this. You may as well buy a new boiler.

not everyone does! and if it just a descale of the hot water that is not a powerflush, although we use the powerflush machine it only takes about 1 - 1.5 hours
we charge £120 to do this job including the chemicals.

 

[Agile]

All of you giving and receiving advice should be aware that removing the MAIN heat exchanger should only be done by a gas registered engineer.

Removing the secondary heat exchanger ( when its a seperate unit ) can be done by anyone.

Completely different techniques and chemicals are required depending on if its lime ( calcium ) based scaling or metal oxide based "scaling" which is better refered to as sludge or dirt.

Hydrochloric acid hardly attacks metals if less than 10% solution and only in contact for a shorter time.

An important aspect is if the product of the chemical reaction is soluble. Sulphuric acid on calcium produces insoluble calcium sulphate. Most chlorides are soluble but iron chloride compounds can be very corrosive.

Tony

 

[stevekane]

Well done Eddie, Im sure its possible to do most of these things yourself with a little thought and cunning. As a follow on from my post above, I removed my domestic heat exchanger and and found it was copper, I then popped along to my local Industrial Chemicals supplier, there are plenty about and I found one near to me through the yellow pages, and he sold me a litre of (I think from memory) a citric acid and that diluted according to his instructions did the trick nicely. The "real" problem however was that I discovered that the "Diverter Valve" was seized, and as a result very little hot water was circulating in the heat exchanger, and this was probably the major reason for the lack of hot water. Once you know about these simple things it ought to be easy for a competant person to realise that the diverter valve was stuck just by touching it,,,such a shame that the then "corgi" registered fitter who serviced the boiler for my son clearly knew more about short legged dogs than my old dog of a boiler,,,or was he bloodhound like on the scent of a nice earner in the boiler change he recomended!!

 

[Agile]

All of you DIYers would be better not to fiddle about with chemicals which will not do the job properly.

Acids are dangerous and body/eye protection is needed.

For lime scale, hydrochloric acid is the best. You can buy it for domestic use in 32% solution as Spirits of Salt and dilute it ( acid into water ) to get about 5-10% solution and use that cold.

I am not encouraging you to use it and lose your eyes, merely telling you what can be used with suitable precautions.

Domestic kettle descaller ( formic acid ) is very weak! It has to be its sold to housewives!

That Worcester Hiflow in the picture above looks ripe for replacement!

Tony