Worcester 28i junior gurgling / metallic bubbling problem

[mr_mason]

afternoon all.

Need some help with my Worcester 28i junior, it's one of the older models, circa 2007.

The pump seized a week or so ago and has been replaced, have a subsequent leak from the aav (from what I can tell) but that's another story.

pressure sits fine, HW works fine, problem comes when firing up the CH, on start up we get a, sometimes loud, almost metallic gurgling and bubbling noise coming from within the boiler and the pressure needle fluctuates, almost vibrates while the noise is present. After a short period of time (less than a minute) the boiler runs perfectly, makes no noise, happy as Larry. To add to the intrigue, when the CH is making its funny noises, if you turn the HW on the noise stops, then when you stop the HW the noise starts up again.

It's just this noise that makes me worry... From doing some reading up it seems the heat exchange is the likely cause but I have a couple of questions.

1. Why would the heat exchange now cause a problem when it was fine before the pump went?
2. What exactly is the problem? Is the heat exchange generally knackered or is there air stuck in there somewhere?
3. Can you vent the heat exchange at all? There is no air in the CH system, all rads and the pump have been bled.
4. Is this issue likely to cause a failure on another part of the system? Expansion vessel or pressure relief valve perhaps? Don't want to start throwing money at a 9 year old boiler unless I know what the problem is.

Help greatly appreciated.

 

[ianmcd]

Your boiler has what we call a Bi-Thermal heat exchanger some call it a dual pass heat exchanger, basically what happens is when you have a call for CH the pump runs to circulate the water around your radiators and when you run the HW tap the pump is stopped but the burner keeps firing and the energy is transferred into the water coming out of your taps, I would be looking at your pump replacement, I have seen some of the new energy efficient pumps where the impeller is slightly bigger than the origionall and it grinds against the pump body till it heats up

 

[mr_mason]

Hi there.

Cheers for the reply.

As it only makes noise when the pump was running I can see why it may not be the heat exchange after all.

The new pump was a complete unit, new pump head and body. If that makes sense? the new pump came with its own head, I still have the one from the old pump though. Think it would be worth stripping it down again and putting the original pump head on and seeing what happens? Need to have a look at why the aav is leaking anyway.

Would be a blessing of it wasn't the heat exchange.

 

[mr_mason]

Any more ideas fellas?

Anyone know why the new pump could be causing noises and pressure fluctuations?

 

[Agile]

A DIYer should not really be opening the combustion chamber where the AAV is located.

Those boilers are usually fairly reliable.

If the pump seized then the water is probably rather dirty.

Tony

 

[mr_mason]

Hi Tony.

Thank you for the reply, I am fully aware it is actually illegal for a non registered and competent person to open the combustion chamber.

I have a gas engineer friend who did the pump change and will be doing all subsequent work.

As I bought and supplied the pump I'm trying to find out what the noise could be, bad pump, air lock, bad workmanship, did the pump take the heat exchange with it, something else.