Pressure Drop with Hot Water flow - Ideal Vogue S32 Gen 2

[bwel]

Hi there,
I have a Vogue S32 Gen 2 in an empty rental property and noticed that the Boiler Pressure Gauge was high at about 3 bar. It may be that the old Tenants over pressured it with the filling loop, as I’ve certainly only filled it to 1.5 bar historically. I drained down the CH water pressure to about 2 bar from a Radiator point. But I noticed that the pressure went back up after boiler operation. Initially I thought it was heat expansion or pump pressure flow as the whole system had not been used for months. I then drained down a little further, aiming for about 1.5 bar, but did not reach that level. I was a bit puzzled, but through I‘d let it stabilise as the boiler has not been running in the empty property for nearly 6 months though Covid.

Then I tried running the boiler for a bit and switched on the hot water tap, the pressure gauge dropped with HW flow down to about 1 bar. Switching off the HW tap and the pressure rose back up above 2 bar. I thought that with a System Boiler, the HW flow should not impact pressure in the boiler ?
Running the Cold water tap, there is of course no impact on the boiler pressure.

Perhaps my brain is a bit rusty, but surely there should be no link between Boiler system pressure and HW flow in a System Boiler with HW tanks ?

Any thoughts on this ?

 

[John.g]

Maybe a unvented HW Cylinder coil leak?

 

[bwel]

Maybe a unvented HW Cylinder coil leak?

Yes, I was also thinking that could be a cause. The install has two unvented tanks side by side. I’ll have to check if there are any isolating valves to take out each heating coil to retest. I suspect their won’t be any valves though.

 

[John.g]

Just to be sure and assuming leak is both ways maybe consider de pressurising HW tanks and the see if you can pressurise boiler system to say 2.5 bar.

 

[bwel]

Just to be sure and assuming leak is both ways maybe consider de pressurising HW tanks and the see if you can pressurise boiler system to say 2.5 bar.

Yes, it looks like the Heating Coil must have corpses in One of the Unvented HW Tanks.
When I isolate the Cold Water main to the house and then turn on a HW Tap, the boiler pressure drops as the pressure is released. Switching the Cold Water on and the Boiler pressure Gauge goes back up to 3 bar +.

Unfortunately, there are no isolation valves to the coils on the Cylinders. Any ideas how to find which of the 2 Unvented Cylinders has failed ?

 

[John.g]

If the both cylinders are hot or even icy cold and pressurised and you then crack open a drain somewhere on the primary circuit, you may then be able to identify which coil is holed by keep feeling both coils flows and returns, the leaking one then may be hotter or colder then the "good" coil, depending on the cylinder temperature, if you have a common motorised valve then ensure de energised (shut) and just keep feeling the coil returns as close to the cylinder(s) as possible.

 

[bwel]

If the both cylinders are hot or even icy cold and pressurised and you then crack open a drain somewhere on the primary circuit, you may then be able to identify which coil is holed by keep feeling both coils flows and returns, the leaking one then may be hotter or colder then the "good" coil, depending on the cylinder temperature, if you have a common motorised valve then ensure de energised (shut) and just keep feeling the coil returns as close to the cylinder(s) as possible.

Hi John,
I’ve just been looking at this again, but wanted to clarify your suggestion.

What do you mean by ‘crack open a drain somewhere on the primary circuit’ ?

I’ve figured out, I can heat just One of the tanks by manually opening the Zone Valve to that tank and with CH Demand but no HW demand.
Then by breaking in to the Coil Return cct (my filling loop) from the boiler and seeing if hot water comes out, then it must be the heated tank that is failing.
conversly, continuous cold or slightly warm water would be the other (non heated tank) that has a failed coil.
Do you think that will work ?
Thx

 

[John.g]

How do you break into the coil return without draining down the whole (primary) system?, if you do drain it down then you can simply break the coils flow or return connections at the cylinder and see which one is leaking, my suggestion should tell you without draining down the whole system but you will have to establish a small drain off flow to establish which coil.

 

[bwel]

How do you break into the coil return without draining down the whole (primary) system?, if you do drain it down then you can simply break the coils flow or return connections at the cylinder and see which one is leaking, my suggestion should tell you without draining down the whole system but you will have to establish a small drain off flow to establish which coil.

Luckily my Filling Loop connects to the Coil Return path just by the cylinders (picture attached). It has isolation valves on both ends, so I can keep the mains feed end isolated but detach that end of the filling loop to drain / feel it and stil have the other end with a further isolation valve before it taps in to the Coil Return.

As such, I don’t need to drain the Coil CCT, but can use that filling loop valve to slowly release water from the coil circuits to feel for heat.

Hope my explanation makes sense. I’m just waiting for the one tank to heat up.

 

[John.g]

Yes, that sounds good.

 

[bwel]

It did not work as easy as I thought. The filling loop has a check valve on it to stop the heating coil passing water back in to the Cold Main.

Can you think of anyway to determine the leaking coil without draining down / breaking in the primary heating cct ?

 

[John.g]

Isn't there a isol valve at both ends of the flexible hose?, just ensure both shut then remove the hose at at either end, open the valve at the coil end and start draining into a bucket or whatever until you identify the leak

 

[bwel]

Isn't there a isol valve at both ends of the flexible hose?, just ensure both shut then remove the hose at at either end, open the valve at the coil end and start draining into a bucket or whatever until you identify the leak

The isolator at the coil end had a built in double check valve so reverse flow from the filling loop flex is blocked.

 

[John.g]

OK, thought it was at the mains end.......just open any rad vent or whatever so to get enough flow to heat a section of the leaking coil.