Slow pressure drop on worcester bosch boiler

[CarloHeatingEng]

You appear to be new to Diynot but obviously know your onions.
Take it you're gas safe registered?
So why don't you join the CC?

Cheers, appreciated! Yes, Gas Safe registered. How do I go about joining the CC?

 

[denso13]

Cheers, appreciated! Yes, Gas Safe registered. How do I go about joining the CC?

https://www.diynot.com/diy/threads/gas-fitters-only-forum-the-combustion-chamber.114690/

 

[dilalio]

Cheers, appreciated! Yes, Gas Safe registered. How do I go about joining the CC?

As per link sent by @denso13 just submit the details and admin will sort it... Eventually lol.

 

[oliverwilliams18185]

Two months from 1.5 to 1 bar with no visible leak points straight at the expansion vessel. Check the PRV discharge pipe outside first. Tie a plastic bag over the end for a day. If you find water in it, the PRV drips and the vessel lost its charge. You can repressurize the vessel in ten minutes with a bike pump. But if the diaphragm is gone, you need a new one. On 14 radiators a second 12L vessel is not crazy. Fix the one you have first. Nine times out of ten the slow drop is the vessel, not a hidden leak.

 

[Johntheo5]

The PRV has not discharged any water through the outlet into a plastic bag so no evidence of leak there. I could not see any evidence of leakage inside the boiler. And pressure gauge has not dropped it seems to swing between 1.2 bar (cold) to 1.5 bar (hot)

For EV sizing I added up the water volume for all rads (using this calc: https://calculator.academy/radiator-water-capacity-calculator/) then added 25% extra to account for pipework + 20 litres (oil boilers have 20 litres more water than gas) = 77.3 L (rads) x 1.25 (25% extra) + 20 L = 116.7L = 120 L (rounded up)

Using Zilmet EV calculator (https://www.zilmet.co.uk/technical-support/expansion-vessel-calculator/)

Pre charge pressure = 1 bar (I assume 1 bar charge), safety valve setting = 10 bar, height difference = 2.5m, total volume water in system = 120 L, max system operating pressure = 70 degrees C, 0% glycol anti freeze present. Comes out at 4 bar EV


Using https://boilersizecalculator.com/boiler-expansion-tank-size-calculator/, it comes out at 8L EV needed (see attached)

I have a 12L EV (this one: https://www.cityplumbing.co.uk/p/wo...2-litre-expansion-vessel-87161076600/p/448035). So it seems a 12L EV is enough.

Are these online EV calculators undersizing the EV needed? Seems experienced plumbers say that EVs are undersized but these calculators say 12L EV is fine.

If I do need an EV; I have put together a parts list in below table. Is there an in line compression coupling with air vent (for regular air bleed from Return line?) that is cheap? The ones I found were very expensive. Prefer manual air vent over automatic air vent as the AAVs are unreliable.

Part	Website
Isolation valve	Essentials Compression Full Bore 22mm Lever Ball Valve with Black Handle (2870V), https://www.screwfix.com/p/essentia...le/2870v#product_additional_details_container
Drain valve	Made4Trade Compression Reducing Tee 22 x 22 x 15mm (https://www.toolstation.com/made4trade-compression-reducing-tee/p98758), Flume MT Cock Type A 15mm Plain Shank, https://www.toolstation.com/flume-mt-cock-type-a/p96526
Pressure gauge
Expansion vessel	Zilmet Cal-Pro Heating Expansion Vessel, https://www.toolstation.com/zilmet-cal-pro-heating-expansion-vessel/p64278
22mm copper pipe	Wednesbury Copper Pipe 22mm x 2m, https://www.toolstation.com/wednesbury-copper-pipe/p58030
Hand pump (with pressure gauge)	https://www.amazon.co.uk/AMZOON-Pre...jid=1017696792334419725-B089LQNCZF-&hvexpln=0
13 PCS Valve Core Remover Tool Kit with Replacement Presta and Schrader Valve Core,Valve Core Remover Tool Repairing Tyre for Universal Car,Bike and Motocycle (replace Schrader valve core)	https://www.amazon.co.uk/FUZVOL-Rep...ycle/dp/B0DP2NSR82/ref=sr_1_4?s=sports&sr=1-4
Straight coupling with air vent - 22mm x 22mm - Brass	https://www.nexaparts.com/bonfix-co...ight-coupling-with-air-vent-22mm-x-22mm-brass, https://www.bes.co.uk/straight-coupler-uk-compression-22mm-7828/

I've used this (my) decades old spreadsheet which is very easy to use in calculating EV size