bioler for hot water on for an hour and then stops

Wierd! Can you give a bit more information about your system.

Make and model of timer? What thermostats are there, and what temperatures are they set to? What zone valves or 3-port valve do you have?

Is this a new problem, or hasn't it ever worked properly?

Roger

Boiler won't fire up unless the cylinder really needs heating. I doubt it takes an hour to heat it up, so it will be up to temperature at that point. My hot water cylinder is only heated for 30 minutes in the morning.

I agree entirely. However, my interpretation of the original post - rightly or wrongly - was that, if the timer was set for more than an hour, the water didn't heat *at all* - rather than heating for an hour and then stopping.

Roger

is there a cylinder stat ?

Nick

Maybe if you time for more than an hour in the evening, it gets the cylinder properly hot so it doesn't need to fire in the morning?

Christian.

The boiler does fire in the morning, but it won't fire for much longer than an hour. Its enough for 2 showers and then there's no HW until the next day! This was not a problem in the past it only started happening in the last few months. I used to have the HW set for a much longer period in the past and the boiler would come on when either the water cooled down or was used up. I have a programmer (manufactured by LAdnis and Gyr) and the system I believe is a fully pumped one.

The timer is Landis and Gyr, there is a thermo on the cylinder which is a Honeywell L641A. This is a new problem