Siemens RDJ10RF shows incorrect temperature?

Hi there, can anybody shed any light on this problem- we have siemens rdj10rf wireless remote to operate central heating. Problem is the heating won't come on at the moment. The remote box is showing ridiculously hi temperatures like 25 degrees plus when in fact the heating hasn't been on for 2 days now and it's very cold. When I change the comfort temperature to e.g. 28 degrees to make it at least turn the heating on, the little triangle appears as if it thinks it's sending the heating up signal but the boiler itself does nothing. Many thanks for any advice!