Baxi making regular noise after power down

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rt18

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My boiler is about 5yr old and has developed a problem which my boiler engineer is unsure about. I thought I'd describe the issue here to see if anybody knows what the cause might be before we start replacing parts unnecessarily.

Historically, over winter, at the end of each day when the thermostat would switch CH demand off, the boiler would begin regular squeaks and clicks which irritatingly vibrate through the pipework and the radiators. It only did it when it was no longer issuing CH heat (ie in the evening after the thermostat switches off), and the chances of it happening were probably one in five, so it didn't happen every day.

We haven't had the issue for several weeks as the heating has been off for a while, but yesterday we did run the heating for a few hours to dry some clothes on radiators. That was yesterday, and we didn't have CH on today at all, but suddenly the noises are now happening after only DHW demand. After a shower, or washing the pots, the radiators would again being the regular creak-squeak-click noise, pause for 5 seconds, repeat. It would continue anywhere up to half an hour, then randomly stop.

There are no errors codes, the water pressure is fine, and in all other respects the boiler works great.

It's a Baxi Duotec 28 (manual link). Looking at the boiler guts, the noise 'sounds' like the diverter valve being opened, then closed, repeatedly, every 5 seconds or so. It states under Operation (section 3.2, step 4) that after supplying DHW the diverter remains in DHW position. It would only switch back if CH demand were received. But we have the heating switched off, so there's no reason to move the diverter now. The CH demand would be received from the thermostat (we have a Nest Thermostat 3rd Gen, been in for 4 or 5 years and never been a problem). So perhaps this is now faulty? Or maybe the Baxi PCB is faulty?

Or maybe this isn't the diverter valve at all and something else is making this noise?

I'd appreciate any expert insight please on what could be the cause. Many thanks in advance.

This is a link to a video recording of the issue: YouTube
 
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With flap down is there any lights on when it's making the noise
 
Radiators sit on nylon lugs in brackets so they move freely.
Without the lugs you get noise like ting ting or click click on repeat cycle as they cool and contract.
They do make a bit in noise when heating and expanding but this don't always happen because it's so fast to heat and expand.
Not all plumbers bother to fit the nylon lugs. Check yours are on on brackets by looking.

Re drying washing.

Buy a £100 dehumidifier.
Game changer.
We use a summer fan with it as well to move air and setup in our small bedroom.
It's faster drying.
Cheaper than heating.
No condensation in house
No rusty rads
 
gas112 said:
With flap down is there any lights on when it's making the noise
Click to expand...
Thanks for your reply. No lights are visible, so CH and DHW demand are off, I guess. You can watch the video I linked to, it shows only the temperature on the display.
 
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Wayners said:
Radiators sit on nylon lugs in brackets so they move freely.
Without the lugs you get noise like ting ting or click click on repeat cycle as they cool and contract.
They do make a bit in noise when heating and expanding but this don't always happen because it's so fast to heat and expand.
Not all plumbers bother to fit the nylon lugs. Check yours are on on brackets by looking.
Click to expand...
Hi Wayners,
The noise issues from the boiler itself, and carries over the pipework throughout the house. Currently the noise occurs after DHW demand only, the radiators (and associated CH pipework) are not hot, so there's no expansion nor cooling happening. It's very regular (please listen to the video recording) whereas expansion noises start fast then slow as the rate decreases. I'm 99% certain I have a component inside the boiler making this noise, probably a mechanically moving part such as the diverter or perhaps the pump.

Thanks for the advice about a dehumidifier.
 
rt18 said:
We haven't had the issue for several weeks as the heating has been off for a while, but yesterday we did run the heating for a few hours to dry some clothes on radiators.
Click to expand...

Drying washing indoors, particularly on radiators, is a really bad idea. It rots radiators, and massively increases moisture levels in the home.. If you must dry indoors, do in a closed room, using a dehumidifier.
 
The noise is definitely coming from the diverter. I tested the supply and it's correct (pins 5 & 7 are 240V) when there's no CH demand. But the diverter motor is constantly running, making clicking noises and whirring noises, occasional squeaks.
1000029488.jpg
 
I don't know if a diverter motor should keep running, 24/7, or whether it should recognise the valve position and stop turning when it reaches the desired position. This diverter motor seems to be running forever.
 
The manual reads to me like the diverter operates when there is dhw demand, the default is ch position. Likely the flow sensor is giving a faulty signal or the PCB is misinterpreting. It's also possible you have a leak on the dhw side, would expect it to be noticeable though if it's calling the valve. Normally you need 1-2 lpm flow to operate the flow switches, not clear how this one works though
 
Interestingly, if I turn on the CH demand the voltage supply to the diverter correctly switches to pins 5 & 6, and the diverter motor stops making any noise. I'm guessing it's driven to the other valve position and stopped driving.
When I turn off that CH demand, wait 3 mins for everything to settle, then request DHW, the voltage to the diverter switches back and the diverter motor starts driving the opposite direction (correct), but keeps driving that way forever. It doesn't stop like it did when it was in the CH position.
 
trojanhawrs said:
The manual reads to me like the diverter operates when there is dhw demand, the default is ch position. Likely the flow sensor is giving a faulty signal or the PCB is misinterpreting. It's also possible you have a leak on the dhw side, would expect it to be noticeable though if it's calling the valve. Normally you need 1-2 lpm flow to operate the flow switches, not clear how this one works though
Click to expand...
The diverter valve does not return by default to any particular position, it is driven to the position by a supply voltage. For domestic hot water, 240 volts are seen on pin 7, and for central heating that supply is moved to pin 6. This suggests to me the diverter valve needs driving in both directions, and there is no default per se.
The thing that I am seeing, or hearing, is when in central heating mode the diverter valve moves correctly to the central heating position and stops making noise. But when in hot water mode, the diverter valve moves to the other position and the drive keeps going, which is where the noise appears to be coming from. I wouldn't expect a diverter valve to keep driving forever, this would suggest it would run endlessly throughout summer when the central heating is off and only hot water is required. I only thought it would drive whilst in motion, and cease when the valve position is reached. I do not know how the diverter controller detects that the valve has reached the correct position to stop driving. Is it possible to detach the controller motor from the top of the diverter valve without having to drain the boiler?
 
trojanhawrs said:
The manual reads to me like the diverter operates when there is dhw demand, the default is ch position. Likely the flow sensor is giving a faulty signal or the PCB is misinterpreting. It's also possible you have a leak on the dhw side, would expect it to be noticeable though if it's calling the valve. Normally you need 1-2 lpm flow to operate the flow switches, not clear how this one works though
Click to expand...
I checked the hall effect sensor on the domestic hot water supply side and it is okay. It has a red neon light which illuminates when it detects domestic hot water demand, and I only see it light when I open the tap, it never lights otherwise. Thank you for helping me rule this out.
 
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