Boiler kettling, is it the heating pump?

T

Timgear

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Hi all!

I had a new Viessmann boiler installed in February this year, they preformed a full power flush etc according to the manufacturers instillation specification and the I staller was manufacturer approved.

We've recently been using the boiler and it's making a whiring noise (kind of like a Flymo lawnmower out a closed window)

I called the installer and they said to book a manufacturer warranty repair.

We had the repair man out today (I was at work so couldn't talk to him but he said it's not the boiler that's the problem, that there is sludge in the system (not really possible in my opinion as it was flushed 9 months ago) and that the pump was noisy causing poor circulation and the boiler to 'kettle'. His remedy was to turn the temperature on the boiler down from 60 to 50 degrees. But didn't give any further information of what needs doing other then we need to get someone else out.

I checked the pump and it does have air in it but the radiators are all getting warm and I have just bled each in case of air in the system, none of them had any air in them.

I did a bit of research and everywhere I looked said the boiler would shut off if it kettled with the built in fail safes however this hasn't happened & the boiler happily plods on with the noises and the radiators (at the original 60) were hot to the touch but not burning.

I've looked for a new pump to replace the old one but I don't want to replace this one and have the same airlock problem.

The pump is currently positioned with the flow pointing down to the floor. So I think this is that is causing the air lock problem.

Our system is:
Open vented gravity fed with hot water tank
Hot water only boiler (heats radiators too)
Grundfors ups 15-50 130 pump

The pump I'm looking at is:
Stuart Turner ST 25/80 (180) Circulator - 230v

Am I ok to purchase this pump and swap it out like for like in the current orientation (obs measurements etc to be checked and confirmed)

Do I need to change the pipework to a horizontal approach with a vent off the output end to allow the air to be vented?

Does the pump need to be replaced at all or does it sound more like a boiler issue?

Many thanks!

Tim
 

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How did the water look when you bleed all the air bleeds including the rads? Have you checked the water level in the F& E tank? Is this tank water looking clean. Consider adding an inhibitor for the kettling ( Noise )
 
Last edited:
75pete said:
How did the water look when you bleed all the air bleeds including the rads? Have you checked the water level in the F& E tank? Is this tank water looking clean. Consider adding an inhibitor for the kettling ( Noise )
Click to expand...
All water from the radiators & pump was crystal clear, just checked in the loft and the F&E tank has a bit of slime on the bottom but is clear inhibitor was added on first fill in February, does it need regular topping up?
 
Water crystal clear, new boiler, F&E tank ok but air in pump…. could be connections allowing air to be pulled in to pump, could be the normal sound as be boiler fires as kettling is very obvious sound, a type of banging coming from the boiler. Still could add the noise reducing inhibitor, takes a few day to act when added to F&E tank. Drop the speed down to 11 and see how the system is in a few days would be my actions
 
75pete said:
Water crystal clear, new boiler, F&E tank ok but air in pump…. could be connections allowing air to be pulled in to pump, could be the normal sound as be boiler fires as kettling is very obvious sound, a type of banging coming from the boiler. Still could add the noise reducing inhibitor, takes a few day to act when added to F&E tank. Drop the speed down to 11 and see how the system is in a few days would be my actions
Click to expand...
Awesome, will look into the inhibitor & will drop the speed down! Thanks for your help!
 
A few more queries.

How many rads and ~ total output in kw or BTUs
What was your last boiler & output
What is the exact model of the new Viessmann and its output.
Your 5M pump is probably a bit on the weak side for a heat only boiler, the Viessmann also may have a higher HEX resistance than your previous one.
What is your vent & cold feed arrangement?, is it, from the boiler (flow), vent, then cold feed (no more than 150mm apart) then the pump, pumping downwards (in your case) into the mid position valve?.
Is the magnetic filter on the return to the boiler and are all the returns teed in upstream of it?

Can you read off the boiler return temp with rads in service, if not, just feel the return at the boiler and estimate its temperature.

You might also consider isolating the pump and remove the head, check that both pump ports are clear by backflushing with a liter or so, check impeller vanes clear by pushing a tie wrap though the vanes.
 
One more thing I should have said, run a magnet down the fill/expansion pipe at the tee connection as an extra check for possible blockage down from the F&E tank just in case your pump / system is short of water, don’t think it should be but it takes only a couple of mins so worth doing. Good luck
 
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