H/L reset light on a warmflow boiler

[SimonG]

As DKIA says, top it up then run it and watch the pressure gauge. I would imagine that it will hit 3 bar and dump water out of the pressure relief. I'd be looking at the charge in the expansion vessel or the hose to the vessel.

 

[Best]

As others have already said, have the expansion vessel air charge checked & pumped up first & the systems water charge. Those Warmflow Combis from about 2010 onwards have a pressure switch which cuts the boiler off when system pressure hasn't been kept above 0.3 bar. Yours may be older model. Be careful of the stats, - there are 3 of them, - control stat, high limit stat ( manually resettable only I think ) & another lower limit stat that is automatically reset I think. I have seen these fail & boiler overheating. Check the pumps are working by holding front of them. The pump for the radiators will only start after the hot water end is satisfied.