Heating is pitching.

[karltimber]

hi folks,

am trying to fix "pitching" in my system

The oil fired part of the house is perfect, and an open system.
I also have a back boiler behind an open fire, but when this is lit, the system pitches, ie hot black water comes out of the expansion pipe.

I have checked the pump, that it is running, when the thermostat tells it to. Two questions in relation to the back boiler.
What temp should I have this at --70 deg ???
What setting should I have the pump at - 1,2 or 3 ?

The exp pipe is higher than the header tank, but could the water level in this header tank cause this pitching, ie too much water in the whole system ?

anything else to check,

thx

K

 

[Onetap]

hi folks,

am trying to fix "pitching" in my system

The oil fired part of the house is perfect, and an open system.
I also have a back boiler behind an open fire, but when this is lit, the system pitches, ie hot black water comes out of the expansion pipe.

Pitching is pumping-over in the UK.

The usual cause is bad design or installation, typically the cold feed on the pump inlet side and the open vent on the pump outlet side. The pump generates a pressure difference between its inlet and outlet and the pressure can be translated into head of water. P= density of water x 9.81 x h. The result is the pump sucks water down the cold feed, pumps it up the open vent.

Running the pump on the slowest speed might solve it , or it may cause the boiler to boil.

I'd trace out the pipework. It's quite likely probably arranged thus;

return pipe; cold feed; pump; boiler; open vent; flow pipe.

or thus

return pipe; cold feed; boiler; pump; open vent; flow pipe.

If so, I'd get it rearranged thus;
return pipe; cold feed; boiler; open vent; pump; flow pipe.

Both the open vent and cold feed are safety features and must be adjacent to the boiler's flow and return, respectively, unless they're actually piped to boiler tappings. No valves in either one, not ever.

The flow temperature should be about 82 degC nominally, but you have very little control on solid fuel. Over 85/90 is a burn hazard. The return should not go below 56 degC for prolonged periods or it wil cause corrosion on the fire side.

And test the safety valve as well. New ones are cheap.