Megaflow issues

[Grantplant]

Hoping you can help. I have had 6 visits from British Gas and back to where we started. Issues are:

High pitch whine through pressure reducing vale on cold feed. Still to be changed. Only make this when running hot water.
Hot water heating when turned off on Honeywell programmer so not calling for heat and heating only on. Apparently 2 port valve is working
Hot water coming out of bathroom taps and ensuite taps both located upstairs closest to cylinder. Takes about 2-3 mins to run cold.
Hot water very hot. I have turned down on boiler but no change.
Water has been coming out of tundish on side of megaflow, you can see from staining as hard water area must be intermittent as I have seen it but must be getting to pressurised doing its job?

All started happening about three weeks ago at same time as far as aware.

I was a bathroom fitter for many years so know a bit but not up to you guys standards. Help appreciated as gas engineers are also scratching their heads.

Thanks

Any ideas?

 

[Madrab]

All these issues sound as they should be relatively straightforward to fix with some comprehensive fault finding by and experienced engineer. I'd be getting someone in that knows what they are doing and is experienced with Unvented cylinder and their controls as these guys don't seem to be.

I would also check that they are qualified, ask to see their G3/UVHW ticket.

 

[Grantplant]

Thanks I am doing that with British Gas.

Has anyone got any suggestions?

 

[Stadan20]

Look on the megaflow there will be a 5 step guide on how to replenish the air gap . This will more than likely solve the problem you have in regards to dripping water .. as for the other problems get rid of British gas and get a recommended local qualified engineer to look

 

[Madrab]

If the HW system is running when not calling for heat then it's usually either a programmer or valve switch issue, needs a proper diagnostic.
The whine will probably be the PRV and needs changed
Water temps usually need the thermostat checked and/or altered
Water from the tundish may be an expansion issue and needs the bubble re-charged or in the case of an overheat may need the Hi Limit stat looked at or require the T&PRV to be checked/replaced. May also be connected to the always on HW issue.

Honestly, all these issue should be straight forward for an experienced engineer to correct, if they can't then I'd be asking questions as to why not. Even with the worst case of stripping it all back to scratch and meticulously working through it, then the fault(s) would be found but it shouldn't really require that sledgehammer approach.

edited for typo

 

[Grantplant]

Thank you. I recharged about a month ago and just after it started happening. The prv is definitely the whine. What about hot and cold mixer valves for showers. If turned off could the still let through hot?