Vaillant VHR 24-28C whines for Britain

[grazzy]

Back in March 2000 I had a new Vaillant VHR 24-28 combi CV installed. It worked satisfactorily and fairly noiselessly - we could hear the gentle whooshing of water when the heating was running. Then about a year after, the thing began to make a whining noise which I presume emanates from the pump. What is noticable about this is that the noise takes about five minutes to build up when the heating comes on in the morning which indicates that it results in some way from the temperature of the system as a whole. Once the system has been operating, as soon as the heating comes on again, either because the thermostat says so or the hot water is not being drawn, the whining starts.

I have of course bled the system of any trapped air and I have read some of the other messages but I am not sure what the problem is and why a one year old kettle should start making a fuss. I have tried different settings of temperature to no avail. Also, it seems that pump pressure can be a reason for this type of noise but as far as I can tell, this model of kettle comes with a fixed speed pump (it's a Grundfos with a Vaillant rebrand label seemingly).

Would anyone know how to resolve this problem? What is the root cause?

 

[peter anderson]

Is it a boiler or is it a kettle?

 

[weargas]

switch on the boiler.
wait until the whining starts.
have someone (who was pre positioned) turn off the gas.
does the boiler stop whining within a few seconds???...................limescaled heat exchanger.
does it continue to whine????.............it's mechanical.....pump, fan etc.

 

[grazzy]

To answer an earlier question, the device is definitely a kettle.

On my own initiative I have turned off a radiator and made sure that all other radiators are either completely off or on (so that there is no constriction in the system) with the result that the whining has certainly diminished.

As regards testing by turning the gas off, I think that the system often works with no gas being burned but the pump still circulates the water. If the thermostat turns off, then the furnace stops and the pump continues circulating the water until it reaches some residual temperature that the kettle accepts.

I think it is the pump that whines when asked to perform too much work (i.e., too may radiators, constrictions etc.) which may be because of sludge in the system, worn bearings in the pump, or other constrictions.

Any thoughts?