This usually means something in the system isn’t allowing the boiler and pump to maintain proper circulation throughout the entire heating cycle.
1. The Boiler Cycling Off Too Early
The first thing I noticed was the boiler cutting out quicker than usual. It wasn’t overheating — it was simply reaching temperature too fast because the water wasn’t circulating properly. The boiler heated the water, had nowhere for it to go, and shut off.
That creates the “heats then stops” effect across the whole house.
2. Lockshields Causing Uneven Heat Distribution
One radiator downstairs was fully open and overheating the room quickly. Once that room reached temperature, the TRV shut it off and the system flow changed suddenly, making other radiators drop out.
After adjusting the lockshield so it didn’t overheat first, the entire cycle became more stable.
3. Pump Speed Slightly Too Low
I had this happen in a previous house. The pump was set too low to keep the full system circulating once everything warmed up. The radiators all heated fine at first because the water was cold and moving well. Once the system stabilised, the weak circulation became obvious.
A small adjustment to the pump setting fixed the issue immediately.
4. Air Pockets Appearing Mid-Cycle
Air can shift around the system when the temperature changes. A radiator that bleeds fine in the morning can develop a pocket later in the day. This can stop circulation partway through the heating cycle.
Bleeding the upstairs radiators usually sorts this quickly.
5. Sludge Restricting Circulation After Initial Warm-Up
Sludge behaves differently when the heating first comes on versus when the system is fully warm. In one property I lived in, the radiators heated fine for the first 10 minutes but then cooled because the hot water couldn’t keep circulating through the partially blocked return pipes.
If this sounds familiar, you may also want to check this article:
Radiator Takes Ages to Heat Up
6. What Actually Solved It for Me
Balancing the radiators and adjusting the overheated room’s lockshield stopped the boiler cycling too early. After that, the system kept circulating consistently through the entire heating schedule.
If you’re trying to improve your whole home’s warmth, start here:
How to Keep a UK Home Warm for Cheap (Complete Guide)
