Vokera 20/80 RS Flowmatic DHW Expansion Vessel Pressure

[DP]

Robbie, blowing off at the PRV HAS to be done. How else are you going to know it operates correctly. As a heating engineer who solely repairs boilers, I use this component to drain the boiler. If it leak, well so it be- it gets replaced. It is a safety component that has to be tested when the boiler is serviced.

Drain the boiler to 0 pressure and pump up the expansion vessel AND keep draining the boiler until no more water comes out the vent. Keep pumping until EV pressure is at 0.7 bar. Now pressurise the boiler to 1.5 bar. Vent the white chamber (11mm spanner). Repressurise to 1.5 bar.

CAUTION---LIVE HAZARDOUS VOLTAGES PRESENT

 

[Robbie1980]

Thanks DP, will try this tonight.

Why only 0.7bar though and not 1 like in the manual. If this is from your experience, then i will be guided by you.
Cheers
Rob

 

[Robbie1980]

Guys,

Sorry to keep posting items - it's just i've struggled for an answer on this one.

My DHW expansion vessel has zero pressure in. Nothing in manual and Vokera didn't respond.

Just found this :

DOMESTIC HOT WATER
EXPANSION VESSEL
This vessel is a smaller version of
the heating expansion vessel. But it is
charged to 2 bar. This vessel absorbs
any increase in pressure after the hot
water tap is closed after use. This prevents damage to
pipe work and stops water hammering. Please read the
pressure relief valve.
Always check the pressure and recharge if it is necessary.
If the vessel is at very low pressure or been tampered
with, it will cause leaks at joints on the hot water
line.
Checking the Pressure
On the Domestic Hot Water Expansion Vessel turn off
cold water supply to the boiler.
On the Boiler, it must be EMPTY.
Turn off at the boiler connections and release the system
pressure by opening the pressure relieve valve or
empty the system.

I have checked its pressure when the system is charged, so will do it again when empty, but i can't see it increasing from zero when empty!?
Rob

 

[Robbie1980]

I drained the system fully earlier this evening and the CH exp ves had bugger all pressure in - didn't register on pressure guage but was a small hiss when i put the footpump on. Pumped up to just under 1bar.

Re-filled and vented as described and set cold system pressure to 1bar.

CH been on for 3 hours constant and at a happy 1.6bar.

Worst case is the exp ves need replacing if it loses pressure again.

Thanks for all your advice and especially DP for questioning my amatuer techniques!

Out of interest, i rang Vokera about the DHW exp vessel which i have 0bar in. They said it should have 0.8bar. When the system was empty, i tried gently to pump up the pressure but there seemed too much resistance so i didn't want to do damage.

Thanks again,
Rob

 

[Robbie1980]

Gents - bit more advice please.

The pressure on the guauge is climbing slowly so i believe the expansion vessel is losing pressure. I will re-test the pressure with an empty system to confirm the drop.

Is adding a new expansion vessel something i can do myself? A bit of guidance would be appreciated. With it being hard to see (tucked away) i wondered what type of connection the heating circuit has to the water side of the exansion vessel?

The manual isn't very helpful.
Thanks
Rob

 

[twgas]

pressure on gauge will increase slowly as system is heating up.

to pump up dhw exp vess you would have to turn off cold main and open hot tap-to release pressure-leave tap open, then pump to about 2 bar, because of the small volume of air it vessel its quite common to lose the pressure you'e just put in as you remove pump!!!

 

[Robbie1980]

pressure on gauge will increase slowly as system is heating up.

to pump up dhw exp vess you would have to turn off cold main and open hot tap-to release pressure-leave tap open, then pump to about 2 bar, because of the small volume of air it vessel its quite common to lose the pressure you'e just put in as you remove pump!!!

Yes i understand the pressure will go up with heat. 2 weeks ago i drained system set ch exp ves to 1bar filled system to 1 bar. Heating on and upto about 1.6 then back down.

now cold system pressure is at 1.5bar so having the heating on is causing a system pressure rise as the exp vess is leaking - albeit quite slowly.

Regarding DHW vessel i did run off the hot water taps with mains shut. Not sure if i left hot tap open. Will have to try this again. Seemed to be resistance to pumping with footpump - prob cos of shut tap. Take your point re: small amount of air and over pressurising.

Could this rise on the pressure gauge be caused by using the hot water and no pressure in DHW exp vessel? The reason i ask is that the heating has hardly been on. Only way to check ch exp ves is i to drain and see if its dropped from 1bar - i guess.
Cheers
Rob

 

[twgas]

dhw vessel will not affect ch pressure.

if ch pressure rises when off and filling loop is defo disconnected then the secondary h/ex is most likely culprit, this does not mean vessel has lost its charge.

 

[Robbie1980]

dhw vessel will not affect ch pressure.

if ch pressure rises when off and filling loop is defo disconnected then the secondary h/ex is most likely culprit, this does not mean vessel has lost its charge.

OK understood. If the exp vess is losing its charge thought this could explain the increase with use of the CH?

I should really confirm this first before eliminating the exp vessel.

The exp vess was flat when pressure was rising to 3bar and when recharged to 1bar and heating on for 3 hours maxed at 1.6bar. So if it is leaking slowing, it could well be the exp vess.

Will drain and re-check pressures.
Appreciate your responses twgas.
Rob

 

[Robbie1980]

Haven't had chance to drain the system fully yet, but i measured the exp ves pressure which was 1.8bar - as was the water pressure gauge on the front of boiler.

Let a small amout of air out of vessel and pressure on gauge came down by same amount.

I think this means the exp vess is OK and CH loop is filling somewhere?

The filling loop is disconnected so must be the washers/o-rings mentioned in previous replies. Anyone got any pictures of those areas to help me?
Thanks
Rob

 

[Agile]

You should not have let air out like that.

You should follow the procedure in the FAQ section to repressurise the EXV.

If system pressure rises with the filling loop disconnected then the mains water is leaking into the system water. A quite common fault on your model is for the middle of the diverter valve to be leaking like this. Needs a full replacement or just a tailpiece as DP calls it.

Tony

 

[Robbie1980]

I wasn't trying to re-presurise it. Just pushed the needle on shrader valve to make sure water didn't come and and pressure went down 0.1barg.

Plate HE - is this the secondary heat exchanger?

My boiler is a vokera 20-80 RS Flowmatic.

Not worth changing the previously mentioned washers/o0rings first?
Thanks
Rob

 

[Robbie1980]

If i get a 3 way valve service kit (or reparer can) is there anyone on here around Wakefield/Leeds who will fit the service kit on my Vokera 20-80 RS Flowmatic? I would prefer someone who knows this boiler well.

A rough idea of price would be appreciated and a phone number.

Many Thanks
Rob