Tony Blair has said he still personally favours members of the House of Lords being appointed rather than elected.
MPs and Lords have differed widely on reform
He warned the Commons liaison committee to be "cautious" before trying to "replicate the Commons in the Lords".
In March MPs voted in favour of 80% or all members of a reformed second chamber being elected in the future, but the Lords rejected the plan.
Mr Blair had said he would support a consensus on Lords reform - if one emerged - but the issue is unresolved.
The House of Lords has voted to keep a fully appointed house, voting down other options for reform, including 50-50 elected and appointed split.
Appearing before the Liaison Select Committee for the final time before he resigns as prime minister next week, Mr Blair said his support of a non-election second chamber remained, but he would not be advising his successor Gordon Brown on a way forward.
"He's perfectly capable of making his own mind up on the issue. And if people take a different view, which people do, on this issue, that is entirely justifiable too.
"This is not advice to my successor, this is more comment to my colleagues in the House of Commons: I would just say, 'Be really cautious of trying to replicate the House of Commons in the House of Lords'.
"I don't think that really works," Mr Blair said.
"I think if we want it to be a proper revising chamber it's best for it to be a different type of chamber."