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Think I said this before a couple of posts before. Pump overrun does not play a role here. The boiler has a continuous "go" signal because the room thermostat is not satisfied. Pump overrun will only come into play either when the room thermostat (eventually) is satisfied, or at the end of the...

Up to a point. With a fixed output boiler where you cannot turn down the heat, the only way it can work is to turn the burner on and off. This will always happen as the system and house get up to temperature. But there is an enormous difference between running for five minutes and off for 5...

Thank you, but I'm afraid I have to differ. As you can see from the graph, I have 20°C difference between flow and return as the system warms up from cold. Since Rayburn specifies 10-14°C and plumbers tell me that 11°C is the magic number, the only interpretation is that I have insufficient...

After spending quite a bit on plumbers who did not help, I decided to invest 40 quid in a dual input K-type bead thermocouple digital thermometer. The Rayburn has the flow and return pipes exiting the range on the left hand side. I therefore clamped the two bead thermocouples there. Since I am...

Sorry, I should read the quoted text before replying:-( The pump is in standard mode on the highest speed. I did try proportional mode just as an experiment, but the pump slowed right down and I had the impression the boiler was starting to kettle.

Actually, the manual says that whoever set the output power should have marked the value set on the inside of the boiler door. Must check mine when I get back home.

Think nozzle is asking about the boiler not the pump. Have you downloaded the installation manual? There it describes setting the boiler output by tweaking the gas input valve and measuring gas pressure. In any case there is not a great deal of flexibility and it will be between 17.6 and 23.4kw...

Its is the newer ups2 pump but basicaly the same as a 15-50. Speed is set to max. To be honest I was asuming 20kw for the moment. Think I wil get someone in to adjust it down to 17.6kw. However with my current 20 to 25 acros the boiler it is increasingly looking like a bunged up heat exchanger.

Just to clarify some points. When talking about 75degC I meant flow temp. From cold when both flow and return are 20degC, turning on the boiler will cause flow to rise rapidly to 45degC in about 30 seconds. Then will rise slowly to 75degC over 15 minutes. Return rises to 50degC over same period...

Think picasso could be on to something with system resistance. Maybe a Rayburn system requires a high head pump to overcome the heat exchanger resistance. Resistance curve for Rayburn on dara sheet looks a bit steep. Want to reply more on this but cant till weekend. Away in hotel with 1kbps internet

Hi DP, thanks for your interest. Since my problem turns out not to be the zone valves I have made another post entitled "short cycling rayburn boiler" and put the details answering your questions there.

I have a problem with my boiler, a Rayburn 480ag (gas fired), which is short cycling. From cold it will burn continuously for 10 to 15 minutes until the boiler thermostat turns it off. It is off for just 30 seconds before firing up again, running for 30 secs, turning off again, etc, etc. It may...

Thanks for all the comments, and the answers as to what happens when the valves are the wrong way round. To be honest I am losing confidence in my plumber. When he tells me the zone valves are the wrong way round then I have no reason to doubt him. However, in taking a closer look myself I find...

I have Drayton ZA5 zone valves for hot water and central heating in the house that we have just moved to. Things are not right because the boiler is cycling every minute. Measuring flow and return temperatures indicates that the problem is insufficent flow through the system. The plumber who...