Cheapest backup/test DSL router

I have a suspicion my Zen Fritzbox is being flakey. I seem to have ditched all my previous collection of modems and routers. Is there a cheap reliable test DSL modem/router I could get for testing purposes (getting lots of DSL sync issues).

I would suggest the old faithful Huawei HG612-3B modem, ( which was one of the original Openreach supplied modems) which I have used on FTTC services for years and never had a problem. With unlocked firmware it can give a full range of line statistics. Available on auction sites for not a lot of money. You can connect it to any router with an ethernet WAN port to link to your local network.

If you actually want a single box device then the zyxel VMG8x34-B10A ones are a good alternative.

Good shout on the Openreach modem, just ordered one. Depressingly I took mine to the tip a year or so ago.