Are there any circumstances when this could happen?

[1974stephen]

Are there any circumstances where a two port motorized valve could switch the 'fire boiler' contact, but not actually open in any kind of fault scenario?

 

[seco services]

if the micro switch gets stuck it will send power to boiler to fire up.
perm power on the grey and micro switch stuck will give power to the orange.

 

[Garfeild]

Should also power up the pump,boiler will quickly overheat though lack of circulation,possibly making banging noise,and cutting out on overheat.

 

[1974stephen]

So on planning some changes to my system, my proposed idea of taking the flow from the boiler into two MV's via a T piece, to have two zones on the system, each controlled by their own stat, could cause problems to the boiler in a fault condition?

Is there a sneaky way round this, or is it just a risk you have to take when having such as system?

 

[steve32]

fit a by pass between pump and mv's

 

[dextrous]

As steve says. On the other hand, depending on your current system, there may aready be a bypass.

 

[1974stephen]

Would the bypass be inside the boiler? If not, then we haven't got one.

Does a bypass just consist of a short link between flow and return prior to the MV's or something else?

 

[twgas]

your system will need to be something like this.

 

[1974stephen]

It says I don't have permission to view the file.

From the small view on the main page it appears that the bypass consists of a link between flow and return with no special valves or other fancy bits. Is that right?

If so I've got it, and thanks for the replies.

 

[D_Hailsham]

if the micro switch gets stuck it will send power to boiler to fire up.
perm power on the grey and micro switch stuck will give power to the orange.

I have never seen the sense in having the grey fed from a permanent supply. It only needs to be live when the valve is open, so logically the grey should be fed from the same supply as the brown. This would instantly prevent the boiler firing up due to a stuck micro-switch when the controls were not calling for heat.

 

[twgas]

if the micro switch gets stuck it will send power to boiler to fire up.
perm power on the grey and micro switch stuck will give power to the orange.

I have never seen the sense in having the grey fed from a permanent supply. It only needs to be live when the valve is open, so logically the grey should be fed from the same supply as the brown. This would instantly prevent the boiler firing up due to a stuck micro-switch when the controls were not calling for heat.

This causes a back feed so when both valves open they are kept open by each other even when their own stat shuts off.

 

[twgas]

It says I don't have permission to view the file.

From the small view on the main page it appears that the bypass consists of a link between flow and return with no special valves or other fancy bits. Is that right?

If so I've got it, and thanks for the replies.

You need an auto by-pass valve in the by-pass.

 

[griggs]

From the small view on the main page it appears that the bypass consists of a link between flow and return with no special valves or other fancy bits. Is that right?

If so I've got it, and thanks for the replies.

You need to install an autobypass valve to comply with building regs, a gate valve no longer complies.

 

[D_Hailsham]

This causes a back feed so when both valves open they are kept open by each other even when their own stat shuts off.

Of course . I have just drawn a quick wiring diagram and can see what would happen. You also could not connect the grey to the HW ON or CH ON terminals of the timer as there could be times when the thermostat is still calling for heat, even if the timer isn't. You would then get back feed through the micro-switch and the thermostat in series.

Pity. I've been reinventing the wheel.

 

[twgas]

I was, knowing your electrical knowledge, somewhat surprised at your suggestion, obviously a temporary glitch in the old grey matter