Vaillant 438 open vent boiler noise

[craftor]

A couple of weeks ago I had a downstairs TRV leak so I drained down and changed it

While it was drained I changed a couple of dodgy looking bottle air vents, put in chemicals and topped up. When I turned the mains on nothing happened for a while, I played with the temp control knob and things fired up
Now im left with a motor bike noise when the boiler really goes on full gas

I'm wondering if the boiler is really oversized as I've only got 11 rads, 3 are 1200x 600 doubles, the rest are standard bedroom and bathroom sizes

The 2 front room rads are 22mm teed 15mm, the rest are 10mm micro bore pumped with a Wiko gold
Any thoughts would be appreciated

 

[Agile]

You wonder but I will say that it is severely oversized. Probably a 415 would have been adequate!

I also suspect that you refilled the system without a gas registered person to properly vent air out of the boiler and may have damaged it.

Tony

 

[craftor]

You wonder but I will say that it is severely oversized. Probably a 415 would have been adequate!

I also suspect that you refilled the system without a gas registered person to properly vent air out of the boiler and may have damaged it.

Tony

Thanks Tony. What part might be damaged and is it possible to adjust the KWs when I employ a RGI

Chris

 

[Agile]

With an oversized boiler its not quite as simple as turning down the power.

Depending on your exact model it probably has a minimum power output of about 6.5 kW. The difficulty with that is that most of the time your house will only need say 2-6 kW and the only way the boiler can produce an average power below 6.5 kw is by just turning itself on and off. That is inefficient and puts more strain on the components with so many more startups.

You can reduce the power yourself on the front panel by going to the d0 setting, seeing what it is at and then reducing it to say 16 and saving that and see what effect that then has on the operation. Search this forum and you will see more detailed instructions.

If you were really lucky it might even prevent the noise.

But I fear that the heat exchanger may have been damaged but the only place to properly diagnose a boiler fault is at the boiler.

Who was so foolish as to specify such an oversized boiler? Its suitable for an 8 bedroom detached house?

Tony

 

[wannocks]

You can mitigate this situation but not cure it without changing the boiler. It can be down rated but it will light at around 3/4 of full power so will short cycle whenever the heating is up to temperature. Micro bore pipe work will make it worse. The pump is probably inadequate. This boiler will need a minimum flow rate through the heat exchanger at all times, pump and bypass need to be specced to suit.
The info needed to do this is in the manual.

 

[craftor]

It was fitted by a RGI when my old boiler started leaking, I did have some trouble with him, like I had to phone him up to fit a bypass valve

Would I have any recourse against him after 6 years?

 

[fezster]

I also suspect that you refilled the system without a gas registered person to properly vent air out of the boiler and may have damaged it.

Tony

Could you elaborate on this please? I have had my system drained down and refilled countless times at the beginning of it's life, by multiple RGI's. I dont recall any of them doing anything to vent air at the boiler. I have the same boiler as the OP.

This is a genuine question, btw - I've not heard of this before.

 

[craftor]

Thanks for your input guys, seems like the problem is solved by setting the d0 to initially 18 but seemed to be to gentle a heat so left it at 20. Rads getting nice n hot without the noise
Would you advise ramping it up bit by bit for economy or is it ok as it stands

So grateful

Chris

 

[Agile]

I would recommend leaving it as low as you can commensurate with getting enough heat out of it. Then it will be more efficient.

But who specified such an overpowered boiler?

Tony

 

[craftor]

I would recommend leaving it as low as you can commensurate with getting enough heat out of it. Then it will be more efficient.

But who specified such an overpowered boiler?

Tony

Sorry Tony, should have put my specs on its a 428 but still oversized
Did you want the fitters name? I left it all up to him
I previously had an Ideal Mexico rs60, looking at the tables is between 19.5 & 23.1 kW
I suppose he worked off this rating but next size up, being higher efficiency he should have gone down
I had a RGI to look at my problem just before Xmas, all he said I had a too low flow rate and suggested that the zone valves were dodgy then told me to turn down the boiler temp until he come back after Xmas, no sign of him yet
Shame you live in London, I'm beginning to think good heating engineers are hard to come by
Cheers for your suggestions

 

[Agile]

Actually boilers are rated by their output power so should still have been 18 kW however efficient they are or not.

But since Ideal Mexicos were sold, most houses have had significant energy efficient improvements like more loft insulation and double glazed windows etc. So the heat requirement has usually lessened.

But while the power of the previous boiler should be noted, a calculation should always be done. But many heating engineers can walk into a property, look round and state the likely power needed.

Tony

 

[Steelmasons]

But many heating engineers can walk into a property, look round and state the likely power needed.

Tony

That's better Tony.
It's nice to know you are not the only one.