Lime in heat exchanger in a 'new' boiler!

[elizabeth]

In January 2008 we moved into our newly refurbished home where we had installed a new WOLF CBG-50 combi boiler. It was the coldest weather snap in 20 years and within a week the boiler had broken down. The main UK dealer sent out a plumber and after 10 days of robbing boiler parts from around the UK they admitted defeat and agreed to our request for a 'new' boiler. This took a week or so and was then fitted. All was well until about six months ago when the boiler started to shut down if the temperature was set at above number four. We again called the main dealer who sent out a third party plumber (who is excellent). He replaced a thermostat and asked if anyone had been 'messing' about with the boiler (the answer to which is no) as there were a couple of parts which hadn't been fitted correctly. Changing the thermostat didn't resolve the problem and on inspecting the heat exchanger there was a considerable amount of lime. The boiler has been in service just over two years. The UK dealer has declined to replace the heat exchanger and has quoted £800 to replace it. I have checked with the local water authority and whilst average water hardness is scaled at 27.00 we have a rating of 10.8 - very soft water. I am becoming very suspicious that our replacement 'new' boiler is not new but reconditioned. Can anyone offer any help or guidance?

 

[diamondgas]

Hi elizabeth,

My first question to you would be how does the inside of your kettle look? reason being that that'll let you know if you have issues with hard water or not. If that's scaled up with a load of lime then likelihood is you have hard water problems.

I'm not familiar with the make of appliance you're talking about ... Which stat was replaced? Hot water sensor or central heating sensor, Does the problem occur when your central heating is on, when you're running hot water, or both?

 

[stevetheplumber]

a main heat exchanger will not suffer scale and a plate dhw exchanger shouldnt cost anywhere near that

 

[diamondgas]

Okay just checked out the Wolf CBG-50. The litrrature I've got states that the boiler is a condesing system boiler and not condensing Combi as you've stated. Do you have a cylinder fitted. I vaguely remember working on one of these some years ago and if it's the same then it's linked to an unvented hotwater cylinder. Doesn't help resolve your "scaling" issues but does change the potential costs for repair as 'stevetheplumber' points out ..

 

[FD Powerflow]

Get hold of some Kamco FXC2 or Fernox DS40 from your local plumbing merchants, get the installer to come back and remove the heat exchanger, put hex in a bucket, boil the kettle and add one of the above to the boiling water in the bucket. This will dissolve the limescale which affects the temp sensor by telling the boiler that the surface of the hex is reaching temperature but the scale coating it means that the water passing by does not take the heat as efficiently. Even 1mm of scale across a hex will result in a drop of about 12% of the hex output which can negatively affect your gas bill. Dont forget to neutralise the cleaner and give it a good rinse before putting the hex back into the boiler though.

Also if it is a scale build up try getting your installer to add a combi mate or electrolytic scale reducer.