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Bosch Greenstar Combi 151p Boiler not heating and no pressure

guidoism Member Posts: 1
Our hot water heater / boiler stopped working recently. I'm not actually sure when it stopped working since we are not living there due to a renovation. The water heater is new, it's a Bosch Greenstar Combi 151p Boiler set up to provide hot water and to also provide supplemental heat to the heat pump's air handler.

I've read all of the documentation I can find and have narrowed the (or at least the first) problem down to there being zero pressure in the dial as pictured below.

I cannot for the life of me figure out how to re-pressurize the system. The documentation mentions this but doesn't describe the process. This is what the bottom of the unit looks like, looking up:

The five pipes from left to right are: 1. Supply, 2. DHW, 3. Gas, 4. Cold water, 5. Heating return.

I would like to learn how the system works to be able to troubleshoot and fix this myself. I understand that supply is the cold water coming in. DHW is the hot water going out to the fixtures. Gas is the fuel. I don't know what cold water is for and I would think that heating return is the hot water that was used for heating comes back to be re-heated.

So, any thoughts?

How do I re-pressurize this system?

And while I'm here, what are the two pipes on the right for (cold and heating return)?


  • kcopp
    kcopp Member Posts: 4,432
    A picture from further back would help us ID the fill valve. Its not on the boiler itself.
  • Ironman
    Ironman Member Posts: 7,376
    Being renovated?

    Did someone shut a valve or line that supplies water to the boiler?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • psb75
    psb75 Member Posts: 833
    DId you want some help from this forum? It works best if you respond. It could be something very simple. But it requires a modicum of exchange.