If you are using split wireless bands/names, log into the VM hub and see which frequency the gateway is connected to. Should be something like Advanced Settings>>Security>>MAC filtering which should show you your connected devices and what frequency the gateway is connected to in the hub admin pages.
The wireless signal strength at the gateway will be influenced by the layout of your home and the position of the hub/gateway in relation to each other and any obstacles in the way. It is quite likely you will find the 2.4GHz band may give you a higher signal strength but lower connection speed and 5GHz may offer the potential for higher speeds but maybe a lower signal strength. The 2.4GHz frequency may also be more congested. You could use a wifi scanner app to find which band gives you best signal strength and lowest channel congestion and set the hub up for that for the gateway to connect to. The speed of the connection is probably less important for a heating controller device compared to signal strength/reliability. Try it for a bit and see if the connection holds up any better.
The other feature on the VM hubs which regularly seems to cause problems is 'Smart Wifi'/'Channel Optimisation' (see screenshot from newapollo below for a Hub 5, other hubs should be similar)
Hub 5 channel settings | Virgin Media Community - 5591968
this is supposed to dynamically switch the hub to channels which are less congested but some devices seem unable to cope with this and disconnect when smart wifi is on.
You could try turning off the Smart Wifi feature and see if the connection holds up any better by manually setting a non-congested channel or leaving the auto feature on (but without smart wifi).
What version of Hub are you using? The latest Hub 5 seems to have most problems with simple IoT devices.
