Hot water noise, tapping / knocking

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We have a conventional boiler system, small tank in the loft, hot water cylinder in upstairs cupboard with pump and Y port valve and boiler downstairs.

Earlier this year had new timer / control unit fitted, new Y port valve, new pump and new hot water thermostat.

Since the beginning of this week the hot water coming on at 5am has made a repeated knocking / tapping sound, starts fairly slow, gets faster, then slows and stops. Sounds to me like pipe expansion against joists or something in the floor. Knocking noise probably lasts 15 seconds in total.

However, it doesn't stop when up to temperature. The noise just repeats every minute or so and it's driving me mad!

Is it pipe expansion or could it be something else? Anything else I can try?

We have a magnaclean fitted above the boiler, I noticed that sounded like running water (air in system?), I got some air out last night but its made no difference. If anything, worse this morning.
 
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If it has only just started happening it is unlikely but possible to be pipe expansion, has any pipewokr been altered or any work carried out in the route of the pipework
 
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If it has only just started happening it is unlikely but possible to be pipe expansion, has any pipewokr been altered or any work carried out in the route of the pipework

No pipework has been altered. We replaced the ballcock on the cold water tank over the weekend too and while the pipework is next to it in the loft space, nothing has changed there.
Bathroom refit also carried out the week prior but again, no changes to pipework related to hot water system and the noise has only started this week, 2 weeks after the work was completed.
 
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Well, no improvement, over the weekend and still none the wiser.

I am a bit puzzled, thinking about it this morning.
I am not 100% convinced it is expansion. As I mentioned, the noise repeats, even after an hour of the system being on so it should all be well up to temperature by then.

It's a tapping / knocking noise that start slow, gets faster and then slows again, also getting progressively louder. it'll repeat every couple of minutes or so and be almost identical in duration and characteristic.

Any other ideas what else it might be please?
 
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Going to keep bumping this thread. Really need some new ideas of things to try.

I've been searching the internet for similar problems and I'm struggling to find any.
I bled all the radiators and magnaclean last night. Only a small amount of air came out and the problem is just as bad this morning.

Any ideas, please?
 
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Pump speed ? - maybe its running too fast ?

I can try it. It's an Evosta pump with proportional speed, so 6 settings to choose from. Last night I turned it up to it's maximum, where we've been running it previously.
Before that we've had it as low as 3/6 but I found the radiators were taking too long to heat up.
 

CBW

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What brand valve was replaced? What brand valve is in now? Are you able to take photo of current setup?
 
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Another update this morning, noise is still there and I think I now understand why it's repeating like it is.

I noticed the pump and boiler turning off and on repeatedly this morning, so seems the boiler is cycling when hot water is running. It's a Vaillant ecotec plus 418 boiler.
I noted S.8 code on the display, this last maybe around 5 minutes before it goes through the ignition cycle etc for another couple of minutes and then repeats.
Additionally, I noticed one S.53 code but this happened about the same time as the heating system firing up and it cleared (then I had to go to work...)

I suspect this is what is giving the repeated expansion noise! I can't understand why it's only started now but at least it seems we're closer.

I've done some more reading on the forum regarding these boilers and codes, seems it's common.

I will note the D0, D1, D2 parameters this evening and consider changing them to see if it makes a difference.

Any other suggestions? How can I calculate the correct output for D0?
 

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