Last November you worked out that your heating requirement is 10kW and you have approx 13kW of rads, but your boiler gives out a minimum of 11kW. Now this is only needed in the depths of winter, when it is below freezing outside. Most of the time the heating requirement is probably less than 5kW. The only way your boiler can produce the low output is by cycling on and off. Every time it starts up, it runs at max output (28kW) but, as the rads can only give out 13kW, the water temperature rises very quickly. The boiler tries to compensate by modulating down to 11kW, but this is still too much, so it turns off. When the water has cooled sufficiently, it starts up and the cycle repeats - as you have found.Latest investigation/info:-
On putting boiler on from cold, all TRV's fully open, the flow pipe from the boiler goes boiling hot, fires for about 30 seconds, then cuts out. I think the pump continues to run for a few minutes and the flow pipe from the boiler goes quite cool. The boiler then fires up again after about 3 minutes. This cycle keeping continuing.
A typical solution looking for a problem to solve.Plumber has fitted new pump, this was not problem.
Wrong, it's all due to the oversized boiler.He thinks that there is a blockage in the pipework as the thermostat is cutting out because the flow is restricted and the boiler thinks that the water has reached temperature.
Waste of money.Around £400 for a power flush but no guarantee that this will solve it. If it doesn't work they will need to cut back the pipework.
Would it be advisable for someone who knows nothing about plumbing or heating to do this?
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local