Solar Thermal Hot Water Alongside a Boiler
Solar thermal panels heat water directly rather than making electricity.
Solar thermal panels heat water directly rather than making electricity. Paired with a twin-coil cylinder they can carry a large share of summer hot water, with the boiler topping up when the sun does not deliver.
Twin-coil cylinder is essential
The solar coil sits low in the cylinder and the boiler coil above it, so the sun heats the whole volume and the boiler only tops the top up.
Glycol and stagnation
The collector loop uses a heat transfer fluid that degrades over time, particularly after stagnation events. Checking it is the main maintenance task.
Controls
A differential controller compares collector and cylinder temperatures, only running the pump when there is genuine heat to collect.
Solar thermal service or revival
If you have panels that stopped contributing years ago, tell us the cylinder and controller type and we will advise.
Questions we get asked
Will it heat my radiators?
Almost never in a domestic UK setting. Solar thermal is a hot water technology here.
What happens in winter?
Contribution drops substantially and the boiler carries the load. That is expected behaviour.
I have inherited a system that does nothing — can it be revived?
Often. Failed pumps, degraded fluid and dead controllers are the usual culprits and are all serviceable.