Noisy megaflo cylinder (whining)

[CraigR]

Hi, hope someone can help with this.
My central heating system has a Worcester gas combi boiler, paired with a nest thermostat and a megaflo cylinder.
When the boiler starts in the morning, the radiators start to warm up ok, but this is accompanied by a loud whining of the pipes attached to the megaflo. (Sounds a bit like chewbacca)
The whining noise last for a few seconds and repeats in cycles.
I have noticed though, that if I boost the hot water, the whining stops pretty much instantly.
I am not getting any gurgling and no dripping in the tundish, so don’t think it needs to be recharged.

Thanks for any advice

 

[CraigR]

..sorry, obviously NOT a combi

 

[Chuck]

I am not getting any gurgling and no dripping in the tundish, so don’t think it needs to be recharged.

I'd try recharging it anyway. Also have the inlet filter checked by a suitably qualified ('G3/unvented') plumber.

What do you mean by "boost the hot water"?

 

[CraigR]

Boost the hot water - the nest thermostat allows me to heat the water as an override to the schedule

 

[Chuck]

Boost the hot water - the nest thermostat allows me to heat the water as an override to the schedule

Am I correct to understand this to mean that the 'boost' uses the boiler to heat the cylinder not a separate electric immersion heater?

If so, you seem to be saying that the noise happens when there is hot water flowing through the radiators but there should be no flow through the cylinder coil. And it does not happen when the cylinder is being deliberately heated either as part of the standard programme or during a boost period.

Does the system have separate zone valves for the central heating (CH) and cylinder heat exchanger circuits? (Post a photo showing the pipework if you are not sure what you are looking at.)

 

[CraigR]

Am I correct to understand this to mean that the 'boost' uses the boiler to heat the cylinder not a separate electric immersion heater?

If so, you seem to be saying that the noise happens when there is hot water flowing through the radiators but there should be no flow through the cylinder coil. And it does not happen when the cylinder is being deliberately heated either as part of the standard programme or during a boost period.

Does the system have separate zone valves for the central heating (CH) and cylinder heat exchanger circuits? (Post a photo showing the pipework if you are not sure what you are looking at.)

Yes, the boost uses the boiler to heat the water, not an immersion heater.

The cessation of the noise when I boosted the hot water is just something that tried in an attempt to find a solution (the hot water schedule and heating schedule are controlled separately), so I suppose what you said in the second paragraph makes sense.

If have two valves (I think I know what you mean) I will send a picture

For what it’s worth, from picture 1, the whining noise ‘seems’ to be coming from where the copper pipe is exposed (rather than insulated) ?

 

[Chuck]

One possibility is that the zone valve that supplies the cylinder coil is not closing properly. See if the section of pipe at the tee-junction between the higher valve and the air vent (drain cock) above it gets hot fairly rapidly when only the radiators come on.

 

[CraigR]

One possibility is that the zone valve that supplies the cylinder coil is not closing properly. See if the section of pipe at the tee-junction between the higher valve and the air vent (drain cock) above it gets hot fairly rapidly when only the radiators come on.

Do you mean the section I highlighted in the picture? This doesn’t seem to get warm.
I also uploaded another image showing the positions of the HW and CH valves

 

[CraigR]

Do you mean the section I highlighted in the picture? This doesn’t seem to get warm.
I also uploaded another image showing the positions of the HW and CH valves

I also found that boosting the hot water doesn’t always work

 

[Chuck]

I also found that boosting the hot water doesn’t always work

Boosting should be limited by a cylinder thermostat/sensor so it's possible that on the occasions it doesn't work the zone valve is not being energised. See if opening it manually is a reliable way to stop the noise. It's not visible in the picture but there should be a spring-loaded lever that you can move across and latch in place to hold the valve open. Unlatch it when you have completed your tests.

Zone valves sometimes make a 'whining' noise when their head mechanism is worn and they are struggling to keep the valve open. With this is mind, try applying manual assistance to the lever on the central heating zone valve when the whining noise is happening.

Does running a hot-water tap have any effect on the noise?

 

[CraigR]

I think this is the most likely solution.
Unfortunately I am now away for a little while, so cannot confirm it is definitely the answer.
I have bought a replacement Honeywell valve controller and will fit it when I get back.
Thanks for all of your help