Risk to combi boiler left running with no water pressure.

[epsilonGreedy]

Because of my lack of trust in the quality of the mains water plumbing supply into the static caravan I tend to shut off the main water stop cock at the site boundary when leaving the site for few days.

 

This time I am more concerned about frost damage to the internal static caravan plumbing (cold, hot and CH radiators). What is the risk if I leave the CH boiler running and also close the mains water  stopcock?

 

My specific concern is that should a hot water tap drip a little while we are away the combi boiler will sense the pressure drop and fire up as it seems to do. In the worst case the combi might be trying to heat up an empty heat exchanger starved of an incoming water feed. 

[joe90]

Caravan with radiators, luxury, when I was a lad....etc etc...(or during my build, f###ing cold)..........(only jealous mate?)

[ProDave]

A hot water dripping will not drop the pressure of the sealed heating circuit, so don't worry.

 

In our 'van I fitted a pressure reducing valve set to 3 bar, because I simply did not trust the cheap and nasty "caravan grade" push fit plumbing to withstand our 6 bar+ mains pressure.

 

When we went away in the winter I just left all the doors and cupboard doors open and left an electric convection heater with a thermostat on right in the middle of the 'van and it seemed to stop anything freezing.

[epsilonGreedy]

2 minutes ago, ProDave said:

A hot water dripping will not drop the pressure of the sealed heating circuit, so don't worry.

 

 

Ok. What about the mains water feed through the combi heat exchanger enroute to the dripping hot water tap. If that circuit drips and runs dry because the mains water stop cock is closed, any potential problem there? I have noticed that opening any tap in the static caravan kicks the boiler into action briefly.

[PeterW]

22 minutes ago, epsilonGreedy said:

My specific concern is that should a hot water tap drip a little while we are away the combi boiler will sense the pressure drop and fire up as it seems to do. In the worst case the combi might be trying to heat up an empty heat exchanger starved of an incoming water feed. 

flow switch needs about 1.5 litres per minute to trigger a combi - it’s a flow switch not a pressure switch. 

[epsilonGreedy]

7 minutes ago, joe90 said:

Caravan with radiators, luxury, when I was a lad....etc etc...(or during my build, f###ing cold)..........(only jealous mate?)

 

Ours is an extra wide one bedroom model which makes space for a bath plus a separate shower cubical. It is too nice hence a lowered incentive to complete the self build.

[epsilonGreedy]

1 minute ago, PeterW said:

flow switch needs about 1.5 litres per minute to trigger a combi - it’s a flow switch not a pressure switch. 

 

 

Ah ah. I suppose I could test this by closing the mains stop cock, opening a hot water tap and then ensuring the boiler promptly gives up trying to heat the zero pressure circuit with no flow.

[PeterW]

Yep - it will drop the pressure then stop.