During a scheduled outage for refueling and maintenance, the reactor, with the new fuel elements already in place, was in the cold shutdown condition. A loss of instrument air (due to loss of cooling of the non-safety related air compressors) led to full opening of a control valve of the residual heat removal (RHR) system, this led to an increase in the RHR pump flow. This pump was shut down by the operator, with the alleged intention of preventing its damage. The reactor stayed for 10 minutes without forced cooling and the reactor coolant temperature rose from 35 deg. C to 37 deg. C. The instrument air supply was restored and the RHR pump was put into service, no consequences were observed.