Problems Thermostats Can Cause to Television and Radio Reception

1. Introduction

This leaflet explains how you can tell whether a thermostat is causing radio or television interference – and, if it is, how you can stop it.

Faulty thermostats can cause annoying interference to television and radio broadcast reception – normally in short bursts, which may recur at intervals. Thermostats switching on and off in central heating systems, refrigerators or freezers can all cause interference problems but, in our experience, thermostats installed in central heating systems are the most common cause.

Sometimes the offending thermostat is found in the house that is receiving the interference, although there have been cases where the source of the interference has been found some distance away.

2. Checking your thermostat

To identify whether your gas-boiler thermostat is the cause of television and radio interference, follow these steps:

i) Take a portable AM (medium/long wave) radio receiver, switch it on, tune it away from a station, then stand it next to the boiler being tested.

ii) Listen to the receiver when the thermostat is about to switch off the electricity to the gas valve. At the instant it switches, you should hear nothing at all or perhaps a faint “click” from the receiver. This indicates that the thermostat is operating correctly, and is unlikely to be the cause of any interference.

iii) Instead of the click, you may hear a loud rasping noise lasting between about half a second and one minute. While listening to the noise, switch off the mains electricity supply to the boiler. If this switches off the noise as well, the thermostat is faulty. (You will notice that when the rasping sound stops, the boiler extinguishes almost immediately.)

To discover whether it is your thermostat that is faulty, make sure that you switch off the electricity supply during the noise or at the time you expect to hear it. The rasping noise indicates that a faulty thermostat is the cause, but it could be a neighbour's thermostat rather than your own.

If you watch the boiler cycle closely, you will usually notice the interference starting just before the boiler switches off, and ceasing at the moment the boiler switches off.

3. The problem

Regulations made under the Wireless Telegraph Act 1949 require thermostats to comply with British Standard BS EN 55014, both when installed and afterwards. We have no doubt that thermostats comply with the Standard when new, but the suppression components become ineffective over time, allowing bursts of broadband interference which affect broadcast reception.

We deal with many cases of interference caused by thermostats or the radio-suppression components fitted to them; in about 90% of these cases, the interference is attributable to thermostats in gas boilers. It seems that, as these operate in a heat-stressed environment, they are prone to more rapid deterioration than other domestic thermostats such as room thermostats, cylinder thermostats and diverter switching valves.

If the interference lasts long enough to disturb the listener/viewer, the thermostat is almost certainly in breach of the regulations. This is not a criminal offence in itself, but it is a regulatory matter for us to deal with. We can serve enforcement notices on owners of substandard thermostats, and it is an offence not to comply with such a notice. A malfunctioning thermostat may also pose a safety risk; for example, a boiler may not turn off at its pre-set temperature.

4. How we deal with complaints

In terms of enforcement, the issue is never as simple as it appears from the above description. The only effective cure is to suppress or replace the thermostat, but first it must be traced. This can be time-consuming, particularly if the interference is to radio reception, as the source may be a considerable distance from the affected equipment.

Even if the interference affects television reception (meaning that the source is likely to be more local), there may be a number of premises near enough to be the cause. Thermostats have been known to cause interference to households up to 90 metres away.

Unless the interference can be traced, which is problematic when dealing with intermittent bursts of a few seconds, it can take time to check each of the possible sources. It is often difficult to identify the offending thermostat, particularly if neighbouring householders are not at home.

For example, we recently received a large number of domestic interference complaints from two housing estates in Hampshire. We found that all the affected houses had the same type of gas boilers and the same thermostats, all fitted when the estates were built and all beginning to break down at the same time.

Our staff have no statutory rights to enter premises in these cases. We can obtain a search warrant, if a magistrate is satisfied that there are 'reasonable grounds' to suspect that an offence is being committed on particular premises. However, an offence is only committed under the interference regulations if an enforcement notice has been served but not complied with.

There is a separate offence of 'deliberate interference' under the Wireless Telegraphy Act, which can apply whether or not a notice has been issued. However, it only applies if we have identified the offending thermostat in specific premises and have encountered deliberate non-co-operation from the householder.

Normally, we would expect to solve cases of thermostat interference by discussion and co-operation, and we would not seek to extend our powers of entry in this area. It would clearly be unfair of us to obtain a warrant to search domestic premises if the occupants were unaware of the problems being caused to neighbours.

5. Asking us to investigate

Dealing with interference to domestic broadcast reception is relatively low-priority work. Our first priority is to investigate radio interference that affects safety-of-life services; our second is to deal with interference affecting business users of radio. However, householders can ask us to investigate interference problems, by completing the form in our leaflet RA179 'Television and Radio Interference'.

Our investigation will be carried out free of charge unless we find that the problem is caused by deficiencies in the householder's own TV or radio installation, in which case a charge of £50 will be made.

If we establish that the problem is caused by a thermostat, we must first trace the premises and then seek the owner/occupier's permission to enter and find the precise source. Householders sometimes refuse to let us in. Even if we are allowed access and the source is identified as a gas-boiler thermostat, we cannot immediately cure the problem as we are not qualified to work on gas appliances; however, we can recommend suitable additional suppression.

We usually resolve cases through negotiation and persuasion with the owner of the offending thermostat, but it can be a lengthy process.

6. Preventing a thermostat problem

Once a faulty thermostat has been identified, you will need a qualified service engineer to fit a new thermostat or, more likely, a new suppressor.

Of course, it would be better if the problem could be prevented in the first place. There are a number of possible solutions:

• a service engineer could carry out a simple check (as described in Section 2) as part of the routine service of your boiler;
• the thermostat and suppressor could be automatically replaced after a number of years;
• manufacturers could tighten the specification of component parts to give thermostat contacts a longer life;
• better suppression could be fitted at the time of manufacture;
• the test method for compliance with British Standard BS EN 55014 could be changed, so that it simulated perhaps ten years' use; or
• the industry could decide, as a longer-term solution, to move to manufacturing solid-state switching devices.

Since 1 January 1996, new televisions and radios have been better protected from interference because they have met new European standards for electromagnetic compatibility. Such sets carry the CE mark. This should improve matters gradually, but there are millions of ageing thermostats that are potential sources of interference.

7. Further information

If you have any queries about this leaflet, please contact the following members of our Enforcement Policy Unit:

Doug Raynes
Tel: 020 7211 0463
Email: doug.raynes@ra.gsi.gov.uk

Neil Marr
Tel: 020 7211 0461
Email: neil.marr@ra.gsi.gov.uk

Other information sheets, including RA 179 'Television and Radio Interference', are available free of charge on our website or from:

Library and Information Service
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London
E14 9SX

Tel: 020 7211 0502/0505
Fax: 020 7211 0507
Email: library@ra.gsi.gov.uk
Website: www.radio.gov.uk

RA 272 January 2003 (rev 6)