What is a deadlock letter from my energy supplier?

The Energy Ombudsman states that a supplier has eight weeks to resolve an issue unless it sends a deadlock letter enabling the consumer to come to the service sooner³. The same gateway appears across the Ombudsman's dispute pages: a deadlock letter received, or eight weeks without resolution, is what allows a case to be registered⁴. Once the letter arrives, the clock changes: the dispute must be escalated within 12 months of receiving it⁵.

What follows is the process, the deadlines, the outcomes the Ombudsman can order, and who is eligible to use it. The service is free to the consumer, and it is separate to Ofgem⁶.

What a deadlock letter is and when a supplier must send one

A deadlock letter is not a rejection of the complaint in the sense of a refusal to engage. It is the supplier's formal acknowledgement that its internal process has reached its limit. Consumer guidance puts it as a letter called a decision letter or a letter of deadlock, sent when the supplier has decided there is nothing else it can do¹. Ofgem's consumer guidance describes the same document as a deadlock letter stating the problem cannot be fixed, or that the supplier believes there is no more it can do².

The letter matters because of what it unlocks. Without it, a household has to let the eight-week period run before the Ombudsman will take the case. With it, that wait is waived. The Ombudsman's own wording is that a supplier has eight weeks to resolve an issue unless it sends a deadlock letter enabling the consumer to come to the service sooner³. The same rule is repeated on the Ombudsman's pages for network operators and for flexibility service providers, where the provider has eight weeks to resolve the complaint unless it issues a deadlock letter allowing earlier escalation⁹.

In practice, a supplier sends one when it has exhausted its options: it has investigated, it has given its final answer, and it does not intend to move further. The letter is the trigger for the next stage rather than a dead end.

The 8-week rule and the 12-month deadline

Two clocks run on an energy complaint, and they are easy to confuse.

The first is the eight-week rule. A supplier has eight weeks to resolve the issue, and if that period passes without resolution, the dispute can go to the Ombudsman³. The Ombudsman's eligibility wording is consistent across its dispute pages: the complainant must have received a deadlock letter, or it must have been at least eight weeks since the issue was first raised with the supplier⁴. The same condition is set out for heat network disputes and for named suppliers on the Ombudsman's raise a dispute pages¹¹.

The second is the deadline that starts when the letter arrives. The Ombudsman states that the dispute must be escalated within 12 months of receiving the deadlock letter⁵. Consumer guidance frames the same limit from the other direction: the step must be taken in less than 12 months from when the decision letter or letter of deadlock is received¹.

So the letter does two things at once. It removes the need to wait out the eight weeks, and it starts a 12-month window in which the case has to be brought. A household that sits on the letter past that window loses the route.

How to escalate to the Energy Ombudsman after a deadlock letter

The route has a fixed order. A complaint has to go to the supplier first, and only then can it move to the Ombudsman. The Ombudsman's guidance is that a consumer must raise a complaint with the supplier in the first instance, and that the service is free if the issue is not resolved after eight weeks or a deadlock letter is received⁸. Ofgem's consumer guidance lists the same triggers: a problem not fixed within eight weeks, a failure to agree how to fix it, receipt of a deadlock letter, or dissatisfaction with the decision received².

When a case is registered, the Ombudsman's eligibility checks require sufficient evidence to support it, including the date the complaint was raised with the supplier, and the supplier name must match the account holder's bill¹³. The same evidence condition appears on the Ombudsman's pages for individual suppliers and heat networks¹⁴.

The Ombudsman describes itself as an independent service, separate to Ofgem, for problems with an energy supplier, an energy broker, a network operator or a heat network supplier⁶. Since 1 April 2025, new legislation has required all heat network suppliers to be signed up to the Energy Ombudsman, which extends the same deadlock and eight-week gateway to communal heating disputes¹⁶.

What the Ombudsman can decide: outcomes, awards and limits

The Ombudsman's powers are corrective rather than punitive. It states that it can tell suppliers to take practical action, such as crediting or cancelling an account or changing a tariff, to make an apology, or to offer a financial award, or a combination of these, and it may make recommendations to prevent the issue happening again⁷.

The financial ceilings are set out in the same guidance: up to £10,000 for domestic energy disputes or up to £20,000 for small business disputes⁷. Those are the maximum awards for energy supplier cases.

The limits are stated just as plainly. The Ombudsman cannot punish companies, dictate how companies operate, or issue fines⁷. That distinction matters to a household expecting a penalty: an award is compensation to the consumer, not a fine on the supplier. Where a case involves a business that is larger than a microbusiness, the Ombudsman's supplier guidance notes that a case from a larger business would not be accepted unless the supplier explicitly requested the Ombudsman to do so¹².

How long resolution takes and what it costs you

The eight-week figure is the supplier's window, not the Ombudsman's. The Ombudsman's guidance is that the supplier has eight weeks to resolve the issue unless a deadlock letter is issued³. The same eight-week period applies to flexibility service providers, again unless a deadlock letter allows earlier escalation¹⁰.

For the consumer, the service is free. The Ombudsman states that it is free if the issue is not resolved after eight weeks, or a deadlock letter is received, provided the supplier was complained to first⁸. There is no charge to the household for registering or pursuing a case.

The Ombudsman's own reporting gives a sense of volume rather than speed. Its H1 2026 data release records that consumers were informed about their right to refer unresolved complaints to the Ombudsman after eight weeks or once a deadlock had been reached¹⁷. The guidance documents summarised here do not set out a fixed resolution timescale for the Ombudsman's own handling, so the practical expectation is that the case runs after the supplier's eight weeks or the deadlock letter, not instead of them.

Who qualifies: domestic, small business and microbusiness consumers

Eligibility is narrower than many households assume. Ofgem's dispute resolution guidance states that only domestic consumers, micro-businesses, and small businesses may apply to the Energy Ombudsman¹⁸. The Ombudsman's own guidance for flexibility service providers puts the boundary the same way: a business consumer that does not meet the microbusiness definition cannot have its dispute considered¹⁰.

The microbusiness test is set out in that guidance: fewer than ten employees, or their full-time equivalent, and an annual turnover or balance sheet no greater than the stated threshold¹⁰. The supplier guidance adds that a case from a larger business would not be accepted unless the supplier explicitly requested the Ombudsman to do so¹².

There is a known mismatch between the two definitions. A business may be treated as a microbusiness by its supplier but not meet Ofgem's definition, and the supplier guidance addresses that gap directly¹². Standard Licence Condition 21BA, in the version dated 17 December 2020, requires suppliers to comply with the domestic customer protections for Micro Business Consumers, reading references to a Domestic Customer as a Micro Business Consumer¹⁹.

For domestic supply, the 150,000-customer threshold appears in the supplier obligation rules: a licence-holder supplying electricity or gas to 150,000 or more domestic customers at the end of the qualification year²⁰. The same threshold is recorded in the ECO statistics, where the number of domestic customers must be 150,000 or more, unchanged between ECO3 and ECO4²¹.

Northern Ireland sits apart. The Energy Ombudsman describes its scope as covering energy suppliers, brokers, network operators and heat network suppliers⁶, but Northern Ireland has its own electricity and gas market and its own consumer body, the Consumer Council for Northern Ireland. The guidance summarised here does not set out a separate Northern Ireland supplier list, so a household there should check which body covers its supplier before relying on the deadlock route.