chrisr
We also own a 27RLSS, so maybe I can help you. The water pump is behind the UDC, and you can access it from that side of your coach. There is a 2x2' panel located near the top of the rear bulkhead, but I would unscrew the 2 screws in the top & bottom of the bulkhead itself & slide it out. You'll have to be careful, as there is a duct hose coming from the furnace that goes behind the bulkhead to heat the area back there. Just work it through the hole as you slide the bulkhead out. You'll be able to see & reach the water pump then. There are some of white hoses down there, one of them is the suction line that is used to winterize the coach, it would go into the jug of anti-freeze, it's not connected to anything. It has a valve on it, and near it, close to the water pump is another white hose with a valve on it. I'm thinking that these valves were left in their winterizing position. Just change the position of the valves, & hopefully the pump will start working. Hope this helps. Right now we are in Donna, TX & will be leaving Monday for the Sweetheart Rally in Kerrville. Not sure where we'll be after that. I see that you are near Houston, if you happen to be in either area while we are there I'd be happy to help if you need it, & show you some mods we've done to ours. Just PM me & I'll give you my cell, if you are interested.