Do you provide your customer with a warranty on the delivery that extends beyond the statutory period –

A guarantee is not an extended liability for defects

This is the distinction on which this entire article is based. Liability for defects addresses whether the performance was duly provided at the moment of handover. A guarantee addresses whether the delivery has maintained its promised characteristics for an agreed-upon period, even if it was flawless at the moment of handover. Both can run concurrently, and if the contract does not regulate the relationship between statutory rights and the guarantee, the customer will usually claim whichever is more advantageous for them.

A guarantee of quality arises from a declaration by the guarantee provider that they will satisfy the buyer beyond their statutory rights from defective performance if the item does not have the characteristics specified in the guarantee declaration (Section 2113 of the Civil Code). The provisions on guarantees also apply mutatis mutandis to a guarantee assumed in connection with a contract other than a purchase contract, i.e., also in a contract for work.

In its judgment 25 Cdo 295/2024 of 30 January 2025, the Supreme Court concluded that when assessing the merits of a right under a guarantee, it is not decisive whether the work was performed without defects, but whether the work retained, for the duration of the guarantee period, the characteristics that it was supposed to retain according to the contractor's declaration (the decision is available in the public database).

The same case involved a fence with a five-year guarantee, in which the contractor undertook that the work would be fully functional and fit for proper use for the entire guarantee period and would retain the characteristics defined in the contract. The court interpreted this wording to cover not only functional but also aesthetic properties, and that the wire should not have corroded, even though it continued to perform its protective function. The scope of the guarantee is always assessed according to the purpose of the specific performance and the wording of the clause, so for production technology, normal visual wear and tear may not constitute a defect.

For suppliers, one practical rule follows from this. The sentence "the work will retain the characteristics defined in the contract" is the most expensive sentence that can be written into a guarantee clause. The second consequence is procedural. A customer asserting a claim under a guarantee does not have to prove that the delivery was defective at handover; they will document the content of the guarantee and the fact that the promised characteristic disappeared during the guarantee period. If the supplier wants to defend themselves by citing an external event, they must allege and prove it themselves.

This is also why disputes over guarantees are won and lost on the text of the clause, not with an expert witness. An expert witness only examines what the clause has named as a guaranteed characteristic, and not what the supplier imagined when signing.

What a guarantee can promise without the supplier even realising it

The law adds interpretative rules to the content of a guarantee, which apply even if the supplier did not think of them. If the guarantee provider guarantees that the item will retain its functions and performance for a certain period under normal use, the buyer has at least the right under the guarantee to the delivery of a new, defect-free item or to the repair of the item (Section 2114 of the Civil Code). In the case of a contract for work, the same rules apply only mutatis mutandis, and the customer cannot demand a replacement work if, due to its nature, the subject of the work cannot be returned or handed over to the contractor.

The words "at least" mean that a guarantee cannot be limited to repair only by mere silence. If a supplier wants to exclude the delivery of a new item, they must explicitly state this in the declaration. The second surprise is that stating the guarantee period or the period of usability on the item's packaging has the same effect. The information on the packaging is therefore not marketing, but a commitment.

The third rule targets inconsistent documentation. If guarantee declarations specify different guarantee periods, the longest of them applies. An offer with five years, a technical sheet with three, and a contract with two thus result in five years by default. This can only be defended against if the contract explicitly replaces previous guarantee declarations and specifies the order of precedence of the individual documents.

The fourth rule concerns advertising. A guarantee also arises from a statement made in an advertisement available at the latest at the time of concluding the contract, and if the content of another declaration is less favourable to the buyer, the content from the advertisement takes precedence. There is only one narrow exception: the advertising statement can be modified before the contract is concluded in the same or a comparable manner as the advertisement was made. An addendum to the contract is not sufficient for this.

When the guarantee period starts and when it gets extended

The guarantee period runs from the handover of the item to the buyer; if the item was dispatched according to the contract, it runs from the arrival of the item at the destination (Section 2115 of the Civil Code). For a contract for work, if the contractor has given a guarantee of quality for the work, the guarantee period begins to run upon handover of the work. A special rule applies to deliveries that are commissioned by someone other than the guarantee provider. In that case, the guarantee period runs only from the date of commissioning, provided the buyer ordered the commissioning no later than three weeks after takeover and duly and timely provided the necessary cooperation.

For technology suppliers, this means that the guarantee can effectively start months later than they expected. The clause should therefore include an agreement on the latest date for commissioning. A practical solution is a dual limit. The guarantee period begins on the date of commissioning, but no later than the expiration of an agreed period from takeover, typically three or six months. Although the statutory postponement assumes that the customer actually provided cooperation, a dispute about precisely that is what the clause should avoid.

The same logic is required for storage. For deliveries that the customer takes over and does not install for several months, it is necessary to stipulate the storage conditions, otherwise defects arising there will fall under the guarantee. The second extension mechanism is repair. If the contract stipulates that the guarantee period is extended by the duration of the repair or that a new guarantee runs for a replaced part, the period can be multiplied for a faulty delivery.

The third mechanism is chaining. A customer who incorporates your delivery into their own product often tries to pass on to you a guarantee corresponding to their own commitment to the end customer. This is a separate negotiation, not a technical detail. When chaining, it is reasonable to stick to two rules. Your guarantee period should not start earlier than the period the customer provides onwards, and it should not be longer than the period you get from your subcontractors.

It is also necessary to distinguish the running of the guarantee period from the statute of limitations. The customer must notify the defect within the guarantee period; the claim itself is then subject to the general three-year limitation period under the Civil Code, which runs from the moment the right could have been exercised for the first time. A supplier who negotiates a guarantee claim for years cannot, therefore, be sure that the claim has expired just because the guarantee period has since passed.

When a supplier is not liable under a guarantee

There is only one narrow statutory exclusion. The buyer has no right under the guarantee if the defect was caused by an external event after the risk of damage to the item passed to the buyer (Section 2116 of the Civil Code). However, according to the Supreme Court, the effects of the environment during the usual and expected use of the work cannot be considered an external circumstance. The argument that a delivery corroded due to the weather will not, therefore, stand on its own if it is an environment that is expected for the given use.

The supplier must arrange for all other exclusions themselves. These include failure to adhere to the prescribed service interval, intervention by an unauthorised person, use of unapproved spare parts, operation outside defined parameters, and defects caused by the substrate or subsequent performance by another supplier. An exclusion only works if it is measurable. "Improper operation" is weak in a dispute; "operation above 85°C inlet temperature documented by the control unit's log" is strong.

Consumable parts are a separate category. The scope of the guarantee is governed by the content of the declaration, so without their explicit enumeration and without stating the expected lifespan, they may fall under a generally formulated guarantee period. For exclusions to work, they must be accompanied by obligations on the part of the customer, the fulfilment of which is demonstrable. These include keeping a service log, operating within defined parameters, retaining records from the control unit, and reporting any intervention by a third party. Without these obligations, an exclusion is one person's word against another's.

A promise that cannot be fulfilled will not save a guarantee

There is a limit beyond which an overly broad promise ceases to be a commitment. In the aforementioned case, the Supreme Court stated that if a contractor were to undertake a commitment to an objectively impossible performance through a guarantee, the arrangement would be invalid in that part. In practice, this means that guaranteeing a condition that a given material in a given environment cannot physically achieve for the promised period is not enforceable. However, a court will not accept this defence based on mere assertion; it must be proven by expert examination.

Relying on this is therefore a bad strategy. A dispute over objective impossibility is more expensive and longer than a correctly written clause and ends with the burden of proof, which the supplier finances. The opposite approach is more sensible: formulate the guarantee parametrically. Instead of "it will retain the characteristics defined in the contract," specify concrete, measurable values that the supplier guarantees to maintain, along with the measurement method.

This also resolves the most common dispute about what is still normal wear and tear and what is already a loss of a guaranteed characteristic. Moreover, a parameter gives the sales team a basis for pricing, as a measurable value can be compared with service data. Our text How to sue for a discount due to a defect in a machine discusses disputes over machinery defects in more detail.

Formulations that do not belong in a guarantee clause

The checklist below is based on deliveries of machinery, technological units, and construction works; for software and for deliveries with regular service, the weight of individual points changes, which is why the lawyers at ARROWS advokátní kancelář assess them separately for each contract. Do not use a general retention of characteristics without parameters. It was precisely this formulation that led, in the aforementioned case, to the guarantee also covering the aesthetic condition.

Do not use a guarantee for "flawless operation" or "trouble-free running." In practice, both are interpreted as a guarantee of the result regardless of the cause. Do not use a reference to "usual lifespan" without a number. In a dispute, this is proven by an expert witness, and the outcome is unpredictable. Do not use a different period in the offer than in the contract. By default, the longest of them applies, even if it was a typo in a technical sheet that no one read.

Do not use a formulation taken from another supplier's contract either. Wording that held up for a delivery of a steel structure behaves completely differently for a control system, because in software, changes in characteristics manifest differently than through physical wear and tear, and disputes are about functionality after an environment update. And do not use a guarantee as a sales argument without calculation. Extending it from two to five years changes the calculation of service reserves, not just the text of the contract.

How much a longer guarantee costs and how to calculate it before making an offer

A guarantee is a price parameter, not a legal formality, and yet it is often set in offers as the last line item that no one prices. This is why the cost only becomes apparent in the third year's income statement, when nothing can be re-invoiced. The basis for the calculation is the expected failure rate of the given component and the cost per intervention. A company usually knows both from service data; what it usually does not know is the number of interventions that will be added by extending the period, because the failure rate does not grow linearly with age.

The second item is the availability of spare parts for the entire guarantee period. For deliveries with electronics, a five-year guarantee is a commitment to stock parts that the manufacturer will have since discontinued, or to replace them with a newer series at one's own expense. This is the item that companies underestimate most often. The third item is the tying up of service capacity. A longer guarantee means that technicians who are supposed to be installing new orders are out on warranty claims for old ones; for busy operations, this is an opportunity cost that is often higher than the repair itself.

The offer should then include a reserve expressed as a percentage of the delivery price and reflected in the margin, not a footnote. If the customer demands a longer guarantee and does not accept the reserve, it is a business decision about the price of the contract, not a concession in the text of the contract. How much of this your offer can bear depends on the lifespan of the components used and whether you also pass the guarantee on to your customers — which is why the lawyers at ARROWS advokátní kancelář assess this with the sales team before submitting an offer.

Before you promise a guarantee in an offer

The first decision belongs to business, not law. A guarantee is a price; a longer period means a higher reserve for service, and that must be included in the offer, otherwise the company will pay for it out of its profit. The second decision is about structure. A single period for the entire delivery is the simplest and most expensive option. Dividing it into structure, consumable parts, and software is extra work that pays off in the first dispute.

The third decision is about documentation. A guarantee is assessed according to the text you wrote, so unifying the offer, technical sheets, and the contract is cheaper than any subsequent defence. Our text The Contract for Work in 2026 summarises the related contexts for a contract for work. Czech companies also supply technology abroad, and the guarantee regime must then be set according to the law governing the contract.

Final summary

A longer guarantee is not an extended liability for defects, but a separate commitment that is assessed according to the text of your own declaration. The article has shown that what is decisive is not the quality of the delivery at the moment of handover, but whether the delivery has maintained the characteristics you promised, and that a single, generally formulated sentence can extend the guarantee to cover a condition that no one expected.

The other half of the decision is about money, not text. Extending the guarantee period is a price parameter with three quantifiable items: extra repairs, stocking spare parts, and tying up service capacity. If they are not reflected in the offer, the company will pay for them from its margin. For management, one decision follows from this, which belongs before the offer is submitted, not after signing. Either the guarantee is formulated parametrically, or it is given generally and the company bears a risk of unknown magnitude.

The cost of incorrect wording will not be apparent immediately, but in the third year, when the first claim arrives that, in your mind, was never supposed to be covered by the guarantee. The lawyers at ARROWS advokátní kancelář prepare and review guarantee and service documentation, negotiate the scope of the guarantee with customers, assess it with the sales team before submitting an offer, and represent suppliers in disputes over claims filed.

If you want to verify what your current guarantee clause actually covers, write to consultation@arws.cz or browse our practice for commercial and manufacturing companies.