Sudden kettling in BOTH heating and hot water

[dave22]

What could be the cause of kettling in *both* the central heating and the hot water? It started all of a sudden (not a gradual increase), a few days after a radiator was replaced and the boiler serviced.

It seems hard to believe that both the CH and hot water pipework in the boiler have become gunged up at the same time.

I have a Worcester Bosch 28 Si II combi which had run silently for 9 years.

 

[Agile]

Blocked or slow pump perhaps?

Have you had the boiler serviced?

Tony

 

[dave22]

Thanks for your reply.

Yes - it is serviced annually by British Gas. They plug something in to take readings (gas emissions I think) and visually inspect it. I don't think they've ever taken anything out from inside.

The kettling lasts for just over 5 minutes when the CH first comes on.

If CH is off, the kettling lasts for 5-10 seconds when the hot water is turned on, then goes away.
If CH is on, the kettling on the hot water happens when the hot tap is turned *off*.

 

[Agile]

That British Gas safety check falls far short of what Worcester expect to be done on a service.

Do you have BG breakdown cover or are you actually paying them for their safety check?

Tony

 

[dave22]

I have their breakdown cover which has been useful on other occasions (I had the PCB replaced a few years ago, a new pressure gauge, couple of leaky radiator joints fixed etc.).

But the included service does seem to be, as you say, more of a safety check than anything else.

I have a £50 excess cover arrangement, but in the small print I am not covered if the problem is due to sludge/scale blocking things up.

Worcester say they will repair any problem for a fixed fee of £262.

Do the symptoms in my second post still sound like a blocked pump? I tried some Fernox F2 silencer a couple of days ago. It hasn't helped the CH kettling much on startup, but it has reduced the noise of kettling when the hot water is used. This seems rather strange... unless the kettling is always occurring in the CH pipework even when it is the hot water which is being used?

Dave

 

[bellairaphon]

It may not be a sludge issue. As the pump is not operated during HW. It may be a gas supply issue. Or perhaps a sensor. Has the lockout light flashed at all requiring a reset?

Nath

 

[dave22]

No, there has been no flashing lockout light, and so I haven't needed to perform a reset.

Dave

 

[dave22]

Spoke to Worcester Bosch technical support - the chap there told me that the Si II combi doesn't have separate primary and secondary heat exchangers - there is just one heat exchanger.

He suspects that scale/sludge is blocking things partially in the CH pipework part of the exchanger, and that this kettles when there is demand for hot water since both CH and hot water are heated together with this system.

I haven't quite got my head round why the hot water kettling occurs as the tap is turned *off* when the CH is on, however. Any suggestions welcome - I am genuinely interested in how these things work.

I'll get someone to look at it soon.

Thanks,
Dave

 

[bellairaphon]

Try some sentinel x800 mega flow cleaner to your system. See if it helps.

Nath

 

[Claire4444]

I had same problem last year. We drained our system heating down and put an inhibitor in the tank, worked fine for a few days then boiler started making another weird noise so arranged for some central heating guy to come and he changed the air mixture was here 10 mins cost £70. Touch wood not done it since.