---
title: Central Heating Not Working? Troubleshooting Guide for Devon Homeowners
canonical: "https://tavistockplumber.co.uk/blog/central-heating-not-working-devon-troubleshooting/"
pubDate: 2026-07-09
author: James Bron
description: Central heating faults follow predictable patterns. This step-by-step guide helps Devon homeowners identify the most common causes — from a tripped thermostat to a failed pump — and decide whether to fix it yourself or call a heating engineer.
tags: [central heating, troubleshooting, radiators, boiler, devon, heating engineer]
categories: [Heating Advice]
---

Central heating systems in Devon homes fail in recognisable ways. Most faults follow a pattern that points clearly to the cause — if you know where to look. This guide walks through the most common central heating problems, what causes them, and what to do at each step.

Note: the checks below are safe for any homeowner. Anything involving the gas or oil supply, the boiler's internal components, or the flue must be handled by a qualified engineer — Gas Safe registered for gas systems, OFTEC-registered for oil.

## No Heat at All — Boiler Running, But No Warmth

If the boiler appears to fire normally but radiators are cold across the whole house:

**1. Check the room thermostat.** The most common cause. A thermostat set below the current room temperature, a flat battery, or a wireless thermostat that has lost connection to its receiver will shut the system down entirely. Check the thermostat setting — it should be at least 2°C above the current room temperature — and replace batteries if relevant.

**2. Check the programmer.** If the heating is on a timer and the programmer has lost its schedule (after a power cut, for example), it may be in an off setting. Reset or override the programme manually to force the heating on.

**3. Check the system pressure.** Most combi boilers require a working pressure of 1.0–1.5 bar when cold. Check the pressure gauge on the boiler — usually a small round dial on the front panel. If it reads below 0.8 bar, repressurise through the filling loop (refer to your boiler manual). If pressure drops repeatedly, there is a system leak that needs investigating.

**4. Check for a boiler fault code.** Modern boilers display fault codes when they lock out. The code narrows the possible causes significantly. Common Devon fault codes: low pressure (water loss), ignition failure (common in oil boilers during winter cold), and thermistor faults (sensor failures).

## Some Radiators Cold, Others Warm

If some radiators are warm but others — particularly at the far end of the circuit, or upstairs — are cold, there are two likely causes:

**Trapped air.** Air in the radiator collects at the top. The bottom is warm (water is circulating) but the top is cold. Fix: bleed the radiator. Use a bleed key on the bleed valve at the top corner. Open slowly until water — not air — escapes, then close. See our full guide: [how to bleed radiators — Devon step-by-step](/blog/how-to-bleed-radiators-devon-guide/).

**Sludge deposits.** Radiators cold in patches — cold at the bottom but warm at the top — indicate magnetite sludge settled at the base, reducing flow. Bleeding will not fix this. A [power flush](/services/power-flushing/) is required if the problem is systemic. Individual heavily sludged radiators can sometimes be removed and flushed off-circuit. See our [power flushing cost guide](/blog/power-flushing-cost-uk-devon-guide/).

**Balancing issue.** If radiators close to the boiler are always hot first and far radiators barely warm up, the system needs balancing — adjusting the lockshield valve on each radiator to restrict flow to near radiators. This is a DIY task but requires patience and a clip-on thermometer.

## Cold Radiators After a Power Flush

If your system has recently been power-flushed and radiators are still cold, the most likely explanation is a stuck thermostatic radiator valve (TRV). TRVs can seize in the closed position, particularly on radiators that have been turned down for years. The TRV pin — visible under the valve head — can be freed by gently removing the TRV head and moving the pin manually. If the pin does not move freely, the TRV body needs replacing.

## Boiler Fires But No Hot Water (and Heating Works)

On a combi boiler, separate faults can affect heating and hot water circuits independently. If central heating works but there is no hot water:

**1. Check the diverter valve.** The diverter valve in a combi boiler directs flow to heating or hot water on demand. A failed or sticking diverter valve can deprive the hot water circuit while leaving heating unaffected. This is a repair job for a Gas Safe engineer.

**2. Check the flow rate.** Combi boilers require a minimum flow rate through the hot water circuit to activate heating. If the hot water tap is partially blocked with scale — possible in Devon's moderately hard water areas — the flow rate may drop below the trigger threshold.

## Boiler Short-Cycling (Firing Every Few Minutes)

A boiler that fires, runs for a few minutes, then shuts off and fires again is short-cycling. Common causes:

- System pressure too high (above 2.0 bar when cold)
- Overheat thermostat triggering due to restricted flow
- Pump running at incorrect speed
- Expansion vessel fault (pressure relief valve opening, losing water, triggering refill and pressure fault)

Short-cycling causes premature wear on the heat exchanger and ignition components. A heating engineer can diagnose the specific cause within one visit.

## Pressure Drops Repeatedly

If the boiler pressure falls below the operational minimum repeatedly, there is a water leak in the system. This may be:

- A weeping radiator valve or TRV
- A pinhole leak in a radiator
- A failing pressure relief valve (PRV) — check for damp around the condensate or overflow pipes
- Microbore pipework corrosion (common in Devon properties built in the 1970s–1980s)

A [leak detection](/services/leak-detection/) survey will locate the source, including hidden leaks under floorboards or within walls.

## When to Call a Heating Engineer

**Call immediately for:**
- Any smell of gas or oil fumes
- A yellow or orange flame visible through the boiler inspection window (should always be blue for gas)
- Carbon monoxide alarm activating
- Persistent fault codes that cannot be cleared

**Call — not necessarily as an emergency — for:**
- Repeated pressure loss despite no visible leak
- Short-cycling that persists after basic checks
- Motorised valve faults (zone valves failing to open or close)
- Pump failure (no flow through the system, pump cold to the touch)
- System-wide sludge (cold radiator bottoms throughout the house)

## Frequently Asked Questions

**Why does my central heating work but my hot water is cold?**
On a combi boiler, the most likely cause is a sticking diverter valve. This requires a Gas Safe engineer — it cannot be fixed by the homeowner.

**Why are my radiators cold at the bottom?**
Magnetite sludge settling at the base of the radiator. Bleeding will not fix this. A power flush, or individual radiator removal and flush, is required.

**Why does my boiler keep losing pressure?**
A water leak somewhere in the system. Check all radiator valves for weeping, and have a [leak detection](/services/leak-detection/) survey carried out if no visible source is found.

**Why is my central heating making a banging noise?**
Kettling — a banging or gurgling noise from the boiler or radiators — is most commonly caused by scale on the heat exchanger or sludge restricting flow. A magnetic filter, inhibitor dosing, and possibly a power flush is the usual remedy.

Our [central heating](/services/central-heating/) team covers Tavistock, Okehampton, Launceston, Yelverton, and the wider Devon service area. For boiler faults requiring immediate attention, our [boiler repair](/services/boiler-repair/) service is available across the area. If sludge is confirmed, [power flushing](/services/power-flushing/) can restore full performance to the system.