Gas Smart Meters: SMETS2 Installation, Prepayment & Meter Exchange Process

Summary

Smart meters replace traditional "dumb" gas (and electricity) meters with units that automatically send readings to the energy supplier via a wireless network, eliminating the need for estimated bills and manual meter reads. For tradespeople working on heating systems, gas appliances, and building services, understanding how smart meters affect the gas supply infrastructure is important — particularly when notifying for new boiler installations, assessing meter capacity, and advising customers about meter location issues.

The transition from SMETS1 (early smart meters, 2012–2019) to SMETS2 resolved the major issue of smart meters "going dumb" when a customer switched supplier. SMETS2 meters connect to the DCC, a national data network operated by Capita, and maintain smart functionality regardless of supplier change.

As of 2024, approximately 60% of UK homes had smart meters installed, with the rollout target pushing towards near-universal coverage. Energy suppliers are legally required to offer smart meters to all customers.

Key Facts

• SMETS1 — first generation; supplier-proprietary communications; "goes dumb" on supplier switch unless enrolled in DCC network (most SMETS1 meters have now been enrolled)
• SMETS2 — second generation; DCC-connected; stays smart on supplier switch; mandatory for new installations from 2019
• Gas smart meter — measures gas consumption in m³; converts to kWh via calorific value (CV) from national grid transmission data; CV typically around 39–40 MJ/m³ in UK
• Communications Hub — SMETS2 includes a separate communications hub that connects to DCC via 2G/3G (GPRS) or MESH network
• IHD (In Home Display) — shows current consumption and cost; receives data from smart meter via Zigbee wireless; included free with installation
• Prepayment (PAYG) smart meter — customer tops up via app, website, or Paypoint/Post Office; emergency credit usually £5; debt recovery automated
• Meter exchange (non-smart to smart) — free to customer; arranged by energy supplier; engineer from National Meter Installation Management (NMIM) or supplier's own workforce
• Meter capacity — expressed in m³/hour (e.g., U6 = 6 m³/hour, standard domestic); must be adequate for total gas appliance load; if new appliances added, may need upgrade
• U6 meter — standard domestic gas meter; handles typical household with combi boiler, hob, and fire
• U16 meter — larger domestic/light commercial; for larger boilers, multiple appliances, AGA cookers
• Meter size assessment — sum all appliance gas rates (kW converted to m³/hr using CV); compare to meter rating; if demand exceeds meter capacity, apply to gas transporter for meter upgrade
• Meter location — gas meters must be accessible for reading and maintenance; regulations specify maximum depth of recess; meters should not be in sealed compartments without ventilation
• RGII — Republic of Ireland equivalent (different standard); UK SMETS2 not compatible with ROI

Quick Reference Table

Detailed Guidance

Smart Meter Installation — Who Does What

Gas Smart meter installation is carried out by the energy supplier or a metering provider contracted by the supplier (commonly Siemens, Itron, Landis+Gyr meters, installed by companies such as Morrison Energy Services, Ovo's Volterra, etc.).

What the supplier's engineer does:

1. Shuts off gas at the meter
2. Removes old meter
3. Installs new SMETS2 meter (same size and position unless agreed otherwise)
4. Reconnects and tests gas supply
5. Carries out a gas safety check (they hold Gas Safe registration for meter work)
6. Pairs the meter with the DCC communications hub and the IHD
7. Verifies the meter is sending readings

What a Gas Safe engineer (plumber/heating engineer) does NOT do:

• Install or remove meters — this is the supplier's sole responsibility
• Modify the meter installation
• Work on the pipework between the street main and the meter (this is the gas transporter's infrastructure)

Gas Safe engineers CAN:

• Disconnect and reconnect appliances from the downstream of the meter
• Size the existing meter to assess whether it's adequate for new appliances
• Notify the customer if the meter appears undersized
• Advise the customer to contact their supplier if a meter problem is suspected

Meter Capacity Assessment

When installing a new boiler or additional gas appliance, check that the existing meter has adequate capacity:

1. Sum the maximum gas flow rate for all appliances that could run simultaneously
   • Boiler: maximum kW rating ÷ calorific value of gas ÷ boiler efficiency. For a 30kW boiler at 90% efficiency: 30 ÷ (10.35 kWh/m³) ÷ 0.9 = approximately 3.2 m³/hr
   • For calculation purposes, use 10.35 kWh/m³ as a conservative UK CV
2. Compare total to meter capacity rating (usually printed on meter body or visible as model number: E6 / U6 = 6 m³/hr)
3. If demand exceeds capacity: advise customer to contact their supplier or gas transporter (National Grid Gas, Cadent, SGN, Northern Gas Networks) for a meter upgrade

A meter upgrade is the gas transporter's responsibility and is usually free to the customer, but may require a waiting period and involves their engineers.

Prepayment Smart Meters

SMETS2 meters can operate in credit mode (pay monthly) or prepayment mode (pay upfront). Smart prepayment meters work via:

• Top-up via smartphone app, website, bank transfer, or at PayPoint/Post Office outlets
• Credit is added remotely — no need for physical top-up key or card in most cases
• Emergency credit: typically £5 available if credit runs out outside business hours
• Debt recovery: if in debt to supplier, a portion of each top-up is used to repay the debt before credit is applied

For tradespeople visiting prepayment customers: if a customer has no gas (boiler won't fire, no hob), check the IHD first — it will show "off supply" or "low credit" if the meter has disconnected due to zero credit. This is not a boiler fault.

Meter Location and Access

Gas meters must comply with The Gas Safety (Installation and Use) Regulations 1998 and the GDN (Gas Distribution Network) connection standards:

Siting requirements:

• Accessible for reading, maintenance, and emergency isolation
• Within a ventilated cabinet or recess if external; or in a dedicated meter cupboard if internal
• Not in a bathroom, bedroom, or under stairs without special dispensation
• Emergency control valve (ECV) must be accessible — typically immediately upstream of the meter
• Meter box should be lockable but with a standard key (utility companies have master keys)

Common issues:

• Meter in a sealed room with no ventilation (fire risk)
• Meter access blocked by customer's belongings or locked gates
• Meter that has been painted over or buried in a renovation — this must be reported and resolved before supply can be used safely

Impact on Gas Work

When replacing a boiler or carrying out gas work where the gas supply must be turned off at the meter:

1. Turn off the ECV (emergency control valve) — the lever immediately before or at the meter
2. Complete the gas work
3. Carry out a tightness test (as per IGE UP/1B)
4. Restore supply via ECV
5. Re-light pilot lights / re-commission appliances

The smart meter itself is not affected by switching the ECV on and off. If the meter loses power (rare — SMETS2 has battery backup), it will re-sync with the DCC when power is restored.

Frequently Asked Questions

My customer's smart meter has "gone dumb" — what can I do?

If the meter was a SMETS1 meter installed before 2019, it may not be enrolled in the DCC network. The customer should contact their supplier to ask about DCC enrolment. If it's a SMETS2 meter that has lost connectivity, it may be a communications hub issue — the supplier's remote team can usually diagnose and restore connectivity without a visit.

As a gas engineer, you cannot fix smart meter communication issues. Advise the customer to contact their supplier.

Can a customer refuse a smart meter?

Yes — energy suppliers must offer smart meters but customers can decline. There is no legal requirement to accept a smart meter. However, suppliers are no longer required to provide traditional (non-smart) replacement meters for free in some circumstances; customers who refuse may eventually have smart meters installed when the supplier deems it necessary for network management.

What is the difference between the gas meter and the service pipe?

The service pipe runs from the main in the street to the meter. Everything from the street main to and including the meter belongs to the gas transporter. The installation pipework (from the meter outlet to the appliances) belongs to the customer and is the domain of Gas Safe registered engineers.

Regulations & Standards

• Gas Safety (Installation and Use) Regulations 1998 — GS(IU)R; framework for all gas work including meter requirements

• SMETS2 Technical Specification — DECC/BEIS standard for second generation smart meters

• The Smart Meters Act 2018 — legal framework for smart metering rollout

• GDN Connection Standards — each gas distribution network has connection and meter siting standards

• IGE UP/1B — Purging and pressure testing for gas installations below 75mbar

• Smart Energy GB — Smart meter information for consumers and installers

• Ofgem Smart Metering Guidance — Regulatory framework

• Gas Safe Register — What Gas Safe engineers can do regarding meters

• BEIS Smart Metering Statistics — Rollout progress data

• gas safe requirements — Gas Safe registration scope and requirements

• gas pipe sizing — Meter capacity as part of pipe sizing

• tightness testing — Reconnection after gas supply isolation

• self employment tax — CIS and VAT for gas engineers