I only signed up for virgin media a few months ago and was told their router had the best wifi signal on the market and would stretch further than my plusnet one.... I cant even get a signal out of the living room yet when if i plug back in my old plusnet routeri get a signal in the whole house and most of the garden! Im unable to use internet upstairs in my bedroom even though its only 10ftaway at most why is the signal so poor and what can do? Even talktalks router10yrs ago had a better signal than this! Virgins response was use a cable..... Seeing as i have tablets and phones i cantand shouldnt have to!
Well whoever told you that the VM Hub had the best wifi signal on the market was being somewhat, shall we say, optimistic!
Now what can be done, VM do offer wifi boosters (wifi extenders which use powerline technology), but these can also be problematic, and to be fair on VM both wifi and powerline can be horribly flakey and unreliable in any situation often due to external influences - interference etc. A better solution would be to use a third party router - as you have found already, your Plusnet router gives a better signal through out the house, which often have better performance. The method is to put your VM hub into 'modem mode' which cuts out all of the routing and wifi features, just leaving it as a cable modem and your own equipment takes over all the former functions.
What you need for this is a DSL router, your Plusnet router 'may' be OK for this - without knowing the model, we can't say, but what you first need to look out for as an ethernet port (RJ-45) marked WAN, if it's just got a conventional little telephone-type socket (RJ-11) then it won't work.
A possible alternative - and again without knowing the model number we can't be sure, is that you may be able to turn the Plusnet router into a simple wifi access point - you would need to turn off wifi on the VM hub entirely, disable certain features on the Plusnet router (DHCP definately), and connect one of its LAN ports to one of the ethernet ports on the VM hub. Might be possible but we'd need to know more details to be sure.
Ultimately your best options is just to purchase your own, suitable router and go down that route.
A DSL WAN port will not work with a Docsis connection, so unless the router has a EWAN port.(you will need a cable capable WAN port.)
However, using the Plusnet router is a good idea if it provided a good coverage before. Bear in mind that the range of a router can vary greatly, depending on it's positioning, it's transmission channel and any change in the local wireless environment, so you may not be necessarily comparing apples with apples
To turn the Plusnet router into a Wireless access point.
Connect a pc by Ethernet cable and log into the router. Assign the router a IP address within the Hub's 192.168.0.xxx DHCP, something like 192.168.0.250, to keep it away from the usual IP addresses dished out by the Hub's DHCP server. Disable the router's DHCP server. Connect the router to the Hub, LAN port to LAN port.
You can turn off the hub's wireless and just use the Plusnet router's wireless, or use the Plusnet router as an additional AP to give you more flexibility taking care they are set up not to cross interfere with each other.