I assume you mean the wifi connection to the network is poor at the back of the house. They wont send an engineer for that - wifi is not guaranteed, connections on ethernet cable are. There is too much variation in customer's wifi environments.
VM's solution now is to supply “wifi pods” (not “boosters”). These are free to customers on the 1GB or Ultimate Oomph packages, and so are worth trying if you are on one of those.
Otherwise, you will be charged £5/month - and at that level of investment you would soon pay off that cost by buying a "better" solution than that and it will be yours to own and use forever.
I have never used VM wifi.
--------------------
John
--------------------
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.