Roger Mills wrote:
On 29/09/2017 21:23, Fredxxx wrote:


Did they have pump overruns in 2003?


Yes - long before that. My c1990 Baxi Solo (still going strong!) has
one. They came in with the physically smaller boilers with aluminium
heat exchangers - designed for fully pumped systems - whose residual
heat could cause them to overheat if the flow stopped immediately when
the flame was cut.

Having said that, the over-run logic on my boiler is somewhat flawed -
and there are some circumstances which can still result in an overheat
trip - so I have added a timer as well.

My (I guess) 1986 (still going strong, but probably not very efficient)
Thorn Apollo has one, but I don't know if it's still contributing to the
overall heating effort. Perhaps I'll notice if/when it breaks?