Valliant Turbomax 824/ 2E Fires up for few seconds when cold water run.

[darren bastin]

Boiler fires up for afew seconds when any cold water tap is run. This has happened since cust removed a small cloak rad. I assume the aqua sensor is picking up movement of water , can it be triggered if there is backflow/reversed flow. Boiler is 8 yrs old . Incoming pressure is 3.5 bar. Any ideas

 

[CES]

I would assume that its reversing the flow, don't know why altering the heating circuit would affect the DHW side. Have they fully opened up the stop valve?
If its always happening then I would consider fitting an non return into the mains feed.

 

[Leo21]

Is it when the tap is turned off? Iff it is it can be shunting into the boiler causing it to fire for hot water. This can be solved by putting a mini pressure vessel on it.

 

[diamondgas]

:welcome: to the forum Darren ... Good advice above

Personally I'd be looking for a 'dead leg' somewhere! maybe the custard drained down the domestic circuit as-well as the heating? Any air trapped in the domestic water pipes has the potential to trigger a flow switch! As CES says, a none return valve will solve that!

 

[darren bastin]

I think the custmer has capped off some pipes somewhere , I will go and replace them with isolation valves bleed off the air and see if that cures it.

 

[Leo21]

Surely a dead leg on the domestic wouldn't do that. And also air in cold mains! have new quarter turn taps been fitted? If so they turn off a lot sharper and could cause this fault.

 

[diamondgas]

Surely a dead leg on the domestic wouldn't do that. And also air in cold mains!

Hi Leo21 ... Any air trapped in the domestic circuit can trigger the flow switch to operate as said! Laws of physics Boils law maybe? lol ... Air will compress and relax when pressure is exerted! If that air happens to be in the hot water side of the installation then water will 'push' and 'pull' up and down the hot pipe as the air is compressed and relaxed depending on what is going on elsewhere! Does that make sense?

 

[Leo21]

Ok makes sense, but its when the cold tap is ran. Something has to be shunting the boiler into life via the cold main. If there's air in the hot why would it make any difference. Please don't think I'm saying your wrong just trying to get my head round it. Every day is a school day.

 

[diamondgas]

Ok makes sense, but its when the cold tap is ran. Something has to be shunting the boiler into life via the cold main. If there's air in the hot why would it make any difference. Please don't think I'm saying your wrong just trying to get my head round it. Every day is a school day.

No probs my friend .. see if i can explain this!

Imagine a pocket of air trapped in the 'hot' pipe somewhere on a combi! At rest the whole system is say 6 bar pressure including the compressed pocket of air! So you flush a toilet (cold pipe only) Pressure may drop in the whole system, hot included, to 3Bar yeh? Well the Air at 6bar wants to relax and does pushing water 'backdown' the hot pipe. that triggers the flow switch. either that or the sudden flow back to re-pressurise the air pocket once the valve is turned off!

Does that make sense?

 

[Leo21]

Urika! So suction on hot pipe.I thought the air pocket would act as kind of buffer softening the shunt as the cold water demand stopped. Like I say every days a school day.

 

[diamondgas]

Urika! So suction on hot pipe.I thought the air pocket would act as kind of buffer softening the shunt as the cold water demand stopped. Like I say every days a school day.

So fitting a NRV on the cold inlet to the boiler stops the problem yeh