Boiler pump running after furnace off - where does the heat go?

We did some major refurbishment on our house about two years ago, including an all-new heating system. Three zones: UFH on the ground floor, traditional radiators upstairs, and a hot water cylinder. It's all heated from a Baxi Megaflow 28HE.

During a recent boiler service, the engineer noticed there was no permanent live to the boiler, so the pump couldn't run after furnace shutdown to dissipate the heat.

We've got the wiring sorted now, but it got me thinking. Our boiler's switched input derives from one of three sources:

Underfloor heating - controlled by timer and room-thermostats; UFH control panel sends a signal to the boiler to turn on when needed.

Radiators - controlled by timer (individual rooms have TRVs, but no electrical thermostats) . We have one bathroom radiator with no TRV to dissipate unwanted heat. Motorised valve for radiator circuit switches on boiler whenever valve is open.

HWC - controlled by timer and cylinder thermostat (discovered last night this has failed, so I'll need to get it replaced). Again, motorised valve for HWC circuit switches on boiler whenever valve is open.

Here's what's puzzling me: when the boiler is switched off electronically, the pump continues to run for three minutes to dissipate heat from the heating element.

However: since the motorised valves to all the heating circuits are off, there is nowhere for this heat to go, other than cycling through 6-8 feet of unlagged pipework in our plantroom before re-entering the boiler.

Is this sufficient to keep our boiler's heating element in good order, or should we look at a more efficient way to dump the excess heat?