Biasi 24SE - central heating on in summer mode?

[bollo1000]

My boiler (approx 4/5 years old) has recently developed a fault. The central heating has started to come on in summer mode. If all the radiators are manually turned off, it stops, however, the boiler still seems on be 'on' and making a noise (no flame is lite, however). Dhw works fine.

Could anyone give me an idea of what might be causing such a problem and a maybe also a rough idea of how much it will cost to fix?

Many thanks

 

[Paul Barker]

I'm not yet that familioar with the foibles of these boilers, so Agile may have the common cause in his head.

In general terms about combis though.

1/ they can seem to come on momentarily when cold water is drawn because a sort of bounce in the water supply momentarily operates the dhw flow sensor, sends boiiler into brief cycle and overrun but doesn't go to ignition.. a nuicance. sometimes a check valve on cold inlet solves it, usual cause is a dead leg in old pipework when converting from back boiler to combi.

2/ the temperature sensor (I think funnily enough on the biasi it is the dhw sensor) is faulty and is puting the boiler into frost protection mode.

3/ faulty radiostats/external controls. I have had quite a few call outs to easystats (a generic radio stat available in mechyanical or digital, which a few manufacturers badge for themselves) which exhibit this behaviour. The test method is to remove the external controls and see if boiler still does it.

4/ if you mean it just gets warm when drawing hot water the diverter valve is leaching. Shut the flow isolation under boiler run a tap, does that fix it? Diverter valve is the problem.

 

[Agile]

Dirt in your system has caused the DHW flow switch gland to leak and short out the demand switch.

The gland and switch need replacing. As the gas valve has to be removed to gain access to these components it is a job for a CORGI engineer.

We would charge £127 inc in London.

Tony

 

[Paul Barker]

Oh yes, forgot that one. Hot return pipe, won't work on heating because it's trying to heat hot water.

 

[Agile]

No Paul, it appears to be working on heating because the rads heat up!

But as far as the boiler is concerned there is a demand for DHW so as the diverter is in the rest position it gives heating instead!

Tony

 

[gas4you]

Dirt in your system has caused the DHW flow switch gland to leak and short out the demand switch.

The gland and switch need replacing. As the gas valve has to be removed to gain access to these components it is a job for a CORGI engineer.

We would charge £127 inc in London.

Tony

Never ceases to amaze me how you can charge so little in the London area and make a living Tony

 

[Agile]

Parts about £25 and takes about 1.2 hours and I dont have to make a living from repairing boilers!

 

[Paul Barker]

Surely motorised diverter is in dhw postition as flow switch is operated and heat excapes down return pipe because flow pipe is shut off by diverter.

 

[mehran]

i was thinking the same thing paul

if it thinks there is dhw demand then it would be move the dv motor to dhw and simply over heat the boiler

 

[Agile]

You two are a little out of date and confused!

He has a 24 S with a brass diverter and a flow switch all operated by the diaphragm unit.

The M90 has the Hall effect DHW flow detector and the motor actuated diverter.

Tony

 

[Paul Barker]

Thanks for the lesson.

 

[Agile]

For the advanced lesson, the magnetic shuttle on the M90 can stick in the DHW demand position but in that case whilst the boiler will keep itself hot it will NOT put any heat into the rads !!!

Tony

 

[bollo1000]

Many thanks for the advice chaps