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Well if you keep having air in there, then that needs to be looked at first, clearly there is a leak and air is being pulled into system. Which pump looses power? Where is the UFH pump installed?

https://www.hometree.co.uk/energy-advice/boilers/vaillant-boiler-error-codes.html F20/f22 seems to be overheating safety codes, check zone valves and pump are working correctly

I've got a 418, it overheating too quick after firing up will be related to flow. 1. Does the boiler kettle? 2. Isolate the pump and remove the head check that impeller is all clear, I've had magniite flakes get stuck in mine and eventually killed it as started to have no torque to move water...

Also some valves will not close the microswitch in the manual setting, I know mine does not as it does not go far enough with the manual lever.

And ive looked over that its a 3-port valve so it never really closes, I was thinking S-plan for some reason. Whichever way there would be flow, either to HW or CH. Can you lock the valve position to CH then shut off the timer and see if the bang happens. @MeldrewsMate what if, the power loss...

You may need ABV to be installed between pump/valves and return flow. Or look inside of valve and see if there is a way to tweak the microswitch so it opens before valve is completely shut.

Check the boiler panel and see what status it's in when you expect it to start. Press i button. If you have multimeter and are competent you could see if there is any output on the boiler trigger from the RX1.

Sounds like your pump is still running when the valve shut, could be the valve switch is lazy and does not cut the pump quick enough before it closes. What boiler is it?

Have you got a ABV? When the boiler stops is there pump overrun or does the pump straight away?

Can you post your D00 setting and also have you checked the D40/41 vs what the actual pipes are at, im just thinking an NTC reading out of spec. Can you dial down the max CH flow temp to 65/70c, from what ive read it still acts as the upper limit for the boiler regardless of modulation.

Looks like there are two versions of the wired sensor. The VRC693 is just a simple thermistor, but the VRC9535 seems to have an extra wire for DCF which is the time signal from Germany but can be received in much of the UK, but for some reason its not sold here that I can see. If you have the...

This is the tech page for the VRC720

Mine is, problem is the label only says VR66 (and manual) so it can be confusing for some. I bought a new after my post you saw previously. Model: 0020135785 Are you sure you are not thinking VR65. Ive checked the spec sheet and it shows allowed model number. (this was the VRT not VRC) but...

This highlights reason for multi-zone. Problem is I live in a old 1910 house, the hallway is as long as the house (7m x 2.5m x 9m) and open to the highest point in the roof and skylight and huge front door. So it can become very misleading for the thermostat, my hallway can be cold but the...

True, but they seem to have removed the "permanent" option which is good. But main thing is being able to set different temps per timeslot. I might end up getting the wireless model as I need to relocate my thermo from the large hallway to the living room. I look at it as buying now and if I...

I was looking at the glow-worm products as they are same as vaillant group, found that they had a much newer controller and thought Vaillant may have it, then came across the VRC720 which was similar but seems they have brought in full timing control called "weekly planner", it can have 12...

I guess their idea is that people maintain a constant temperature throughout the day. The whole ideas behind WC is to maintain the boiler at constant low level of firing, if you introduce multiple temp levels then its going up and down. Does not make sense going back though, I wonder if other...

That is some first rate silliness on the VRC700 timer functionally, they should have just included it exactly as it was and you could toggle between legacy or new way. Nearly all timers ive seen can do temperatures against each timeslot but then again how many times to people change temp other...

I put some rubber tubing over it and yes it changed the frequency and made it quieter. My mum can not hear it, I tend to hear quite high frequencies quite easily. Switchmode power supplies run up around 10khz+ so people start to tail off what they can hear the older they get.

It's marked C which means capacitor, ceramic disk caps are fairly common to buzz and depends on frequency power supply is working and board design. Its not a tantalum one though as those are known to pop. I googled problem and buzzing ceramic caps can emit a piezoelectric effect. I know the...