Rayburn Supreme MF grate bars

[camillitech]

At our last house we used to run a Rayburn on solid fuel. That used to go through a riddle wheel every 6 months or so. When we changed it to wood we stopped having to change them. Our Aga little wenlock is 3 years old & has never had a a griddle change (again with the wood adapter fitted).

Same here with the Squirrel's JM, new grate ever six month on coal or year if careful, haven't fitted one in the six years since we switched to wood only. 

[Baz]

This is a problem seen even in little model steam locomotives. The grate bars need a flow of air to keep the temperature down. You can learn a lot about the dynamics of lighting and retaining a fire when it is only the size of a packet of 20.
I also think during lighting if the cold bars are covered in ash any acids produced will condense out and be held next to the bar by the ash eventually becoming boiling acid which has got be a killer even if only for a few seconds. The sulpur in coal makes potent acid but wood still does the same to a lesser extent.
Finally I think "wood burns best in a bed of ash" is just an old wives tale. Have you ever seen a wood fire that doesn't burn better with a good draught. I think it developed from people observing that while wood can burn inside a layer of its air-porous ash coal ash is smothering.

[laurence4fun]

There's a lot of sense in that Baz.
We have an open fire and we were given a lot of conflicting advice about lighting a fire on a bed of ash. I personally have noticed no difference either way with fires lit on a bed of ash and fires lit on a clean grate.
I have however damaged the grate when allowing a build up of ash under the fire.