Chiller down: protecting product while the engineer's on the way

It's 3pm on a Friday. The glycol chiller on the roof has tripped. The return temperature is creeping up. The jacketed tanks are warming, the blast chiller after the cook line is slowing down, and the chill store on the same loop is two degrees up and climbing.

You ring the refrigeration contractor. They're on another job in Leicester and can be with you "this evening".

Here's what actually goes wrong. The chiller can be fixed in an hour once the right engineer is stood next to it. The damage happens in the hours before they arrive, when nobody on site is sure what they're allowed to touch.

First, is it the chiller or the load?

Before anything else, check whether the chiller has stopped or just can't keep up. Look at the controller. Note every alarm before anyone presses reset. Then check flow and return temperatures.

If the chiller is running but losing ground, look at what changed on the load side. A new product run, a tank filled hot, a door left open on the chill store. On a hot afternoon a chiller that was already marginal can fall over. Our post on hot weather and breakdowns covers that one.

If it has tripped, most of the first checks are things any competent fitter or sparky can do without going near the refrigerant:

• Power and control supply. A tripped MCB or a blown control fuse is the cheapest fix of the day.
• Flow. A low flow trip usually means a pump problem, a blocked strainer or a low glycol level. Our pump fault-finding guide has the order.
• The condenser. Fans running? Coil clogged with fluff, leaves or dust? A dirty condenser on a warm day is a classic high pressure trip.
• The water side. Is the glycol the right strength? Has anyone topped the loop up with plain water?

If you find the cause and clear it, one reset is reasonable. Write down what you found. If it trips again on the same alarm, stop resetting. Every reset without a cause is a guess, and repeated restarts can do more harm to a compressor than the fault itself.

Leave the gas side alone

This is where good intentions cause real trouble. Somebody's got a set of gauges in their van. Somebody else has a bottle of refrigerant left over from a split system.

On a chiller using F gas, nobody without the right qualification should be fitting gauges, topping up or breaking into the circuit. GOV.UK puts it bluntly: "it is against the law to work with f gas if you do not have the correct qualifications" (GOV.UK, F gas qualifications). A category 1 certificate covers all activities. Category 4 only covers leak checks where you don't break into the circuit. Our post on F gas certification explains the categories.

The same goes for who you bring in. If you contract another company to service your refrigeration, GOV.UK says that company must be certified, not only the engineer (GOV.UK, company certification).

And if the fault turns out to be a leak, it must be repaired as soon as possible and re-tested within a month* to check the repair worked (GOV.UK, leak checks).

Buy the product time

While you wait, the job switches from fixing to protecting. Maintenance doesn't decide what happens to the product. Technical or QA do. But they need facts from you, quickly.

In England, the Food Safety and Hygiene Regulations set the general chill holding limit for food that can support harmful bacteria at 8°C*. There's a defence for food kept above that for an unavoidable reason, including "temporary breakdown of equipment", but only for a limited period that's consistent with food safety (Schedule 4). The schedule doesn't apply to every business. Plants approved under the separate animal products rules work to their own controls, so let your technical team make the call.

What you can do is give them a clear picture:

1. Product temperatures, taken with a probe and written down with the time, every half hour.
2. Your honest estimate of when cooling will be back.
3. What can be moved to another chill store or a reefer trailer now, while it's still in limits.

Keep chill store doors shut. Stop loading warm product onto a loop that can't take it. Slow the cook line before the blast chiller backs up, not after. Our post on product on hold in food factories covers the restart side.

A hired chiller is only quick if you planned it

If the repair is going to run past the evening, a hired chiller can save the weekend. It's only quick if someone has already worked out where it connects. You need tie-in points on the loop with valves, a power supply big enough for it, somewhere a lorry can put it down, and a plan for the glycol mix. Without those, the hire unit sits in the yard while your fitter goes looking for flanges.

It's a pressure system too

A larger chiller is also covered by the Pressure Systems Safety Regulations. HSE's leaflet on written schemes lists a vapour compression refrigeration system where the installed power exceeds 25 kW* as an example of a system that needs one (HSE, INDG178). If the repair touches pressure vessels, pipework or relief valves, talk to your competent person before you call it done. Our guide to written schemes of examination explains why.

What waiting really costs

Here's our view. Most sites price a chiller failure as the cost of the repair. The real cost is the product in tanks and chill stores while you wait, plus the line you slowed down, plus the weekend overtime to catch up.

Put that number next to the response time in your refrigeration contract. "Same day" on a Friday afternoon can mean 9pm. If the product is gone by 7pm, the contract didn't protect you. That's the gap to close: a certified engineer who can be on site inside the window your product allows, and a shift team who knows which checks are theirs to do.

What to do on Monday

1. Work out how long your most valuable product can sit in each tank and chill store with no cooling. Write it on the wall by the chiller panel.
2. Write a one-page first check list for the shift: alarms, power, flow, condenser, glycol. Mark the gas side as off limits.
3. Check your refrigeration contractor's response time in writing, and that the company is F gas certified.
4. Find out where a hired chiller would connect, and fit the valves now if they're missing.

* Chill holding temperature, F gas re-test period and PSSR refrigeration threshold correct as of 1 November 2026. Check Schedule 4 on legislation.gov.uk, GOV.UK's leak check guidance and HSE's INDG178 for the latest.