When I do a load of laundry, the house fills up with a smell like sewer gas. It hasn't always done this. The washer has an ouside vent, what should I be checking to find the problem, and how should I fix it
Not sure by what you mean by it "has an outside vent". Do you mean the drain line is vented? I assume you washer discharges to a standpipe (or in wall pipe) as opposed to a wash tub. In that case your vent could be clogged which would cause the water in the trap to be pulled down the drain because of the vacuum created. The vent is there to keep that from happening, if it gets clogged then it causes problems. If the water get pulled out of the trap then there's nothing to keep the gases from coming up trough the drain line and into the house.
Or could the smell possibly be from your water? Sometimes you can get a rotten egg smell from your hot water tank due to the anode rod corroding - or if you have well water like I do its possible that sometimes the water just stinks coming out of the groud. But if your whole house is stinking I'm betting on the vent.
Look around at your floor drains or sink drains. One of them may have dried up. Dump some water down the floor drains or unused sink, shower drains in the basement.
If your laundry is in the basement check the sump to see if it needs cleaning. I had a bathroom with a shower put in the basement and had an episode of sewer gas. The plumbers found when the house was built a trap was not put in the floor drain and was allowing the gas to come in. Now the wash tub has to have a plug in it, the sumps are caulked shut and a cover is kept over the floor drain. This has kept the odor in control. Good luck.
baymee....I can tell you've done work for some big buildings where this is a common problem. What you describe is one of the biggest contributers to sewer odor. A clogged vent also does a number. Bees, birds (mostly from droppings sticking to inside) spider webs, a wayward leaf are common causes.
Is this a new problem ?
It is a recent problem. The washer is on the main floor of the house, and outside there is a real tall pipe that sticks up the side of the house. That is the vent I was talking about. So, how would I go about unclogging it? could I pour drain cleaner down it? It looks like PVC
Just look down it and look for some obstruction. Pouring things inside should not be necessary. It could be a wasps nest, or as I said, a drain that's trap has dried up.