Kerosene Boiler Worcester 12/18 Heatslave "hot water expansion" !

[Harryhound]

This heating system is new to me, in reality about 8 years old and in good condition.

In the tail end of last winter's heating season, I think I shot myself in the foot. With more bedrooms than occupants and a water cost of about £4/tonne,
I had a water meter installed.
It might have been a coincidence, but within days I discovered the boiler was leaking. To be specific the gasket had blown on the valve on the top of the boiler, where the boiler decides to prioritise the hot water over the heating the unit, when (say) running a bath.

I had not realised that the water meter would include a non-return valve, so prior to that installation the expansion of the hot water would simply have passed a small quantity back into the rising main.

Poking through the back of one of the kitchen cabinets, there is something that could be an upturned egg cup suitable for a swan's egg, perhaps a bit smaller than a British standard handfull.

Perhaps this corner cabinet was fitted after the boiler because now I cannot get my shoulders into the cabinet and this thing should be pressure corrected every 6 months. [The air was blue as the plumber and I tried to achieve the required pressure AND then remove the air pump, without its internal bladder going flat again. the plumber was muttering that normally there is enough pipework to absorb changes in pressure, but my hot water is all back to back on the ground floor so minimal in length.].

It seems the way out is to fit another expansion vessel on (say) the bathroom hot pipe where it would be a one-man job to check the pressure?.

Is this a sensible idea and is any particular make recommended?

 

[centralheatking]

Hi Harry, I think to get informed responses you might be best to put up
1. Diagram of your system inc. the position of the components...id flow and return etc. accurately
2. A piccy of the up turned egg cup
Then the experts on PF will be able to really help you
centralheatking

 

[Harryhound]

Many thanks for your prompt reply.
It will take me a few days to reply to all your suggestions as the installation is not at my "Principle Private Residence" as the tax man would have it [bit of a complicated story].
So I did try some googling to see if I could find a picture of said expansion vessel and I also dug out the original manual for the boiler's fitting. [Lots of confusing stuff about the three stages of protection for unventilated hot water cylinders].
Like a gas combi it is kept (re)pressurised by connecting up a flexible hose. [I am used to such a system - as my son's first house had a Volkera and natural gas was powerful enough to power direct hot water.

Then I managed to dig out the original installation manual for the boiler. [I wish I had read this carefully before agreeing to the water meter and wish the water company operative had asked me what sort of hot water system I had before he installed it behind the washing machine in the Kitchen]:

Minimum dynamic mains water pressure for optimum performance 1.5 bar.
Maximum mains fed water pressure 10 bar, if necessary fit a pressure reducing valve.
Where the water main supply has a non-return backflow prevention valve fitted, a mini-expansion vessel must be connected to the mains water inlet pipe between the non return valve and the boiler.
(Mini expansion vessel, part No. 7 716 192 105)
Non-return backflow prevention devices fitted to the mains water supply can cause a pressure build-up which could damage the boiler and other household appliances.

[Interestingly this design of boiler predates what has become the current near boiling point cut out switch as the electrical diagram has an extra sheet showing August 2009 (FD code 998) modifications]

I will try phoning the Worcester Bosch helpline tomorrow and see if I can find intelligent life and report back.

 

[Harryhound]

After a bit more research, I discover the mini expansion vessel is very similar to one of these:

BES.co.uk | Next Day Delivery On 15,000 + Plumbing Supplies

Order expansion vessel shock arresters and other expansion vessel accessories online at BES. Low prices. Free next day delivery available. P/N: 11355

www.bes.co.uk

There are lots of similar designs and they are usually used to "cure" water hammer.
It seems that not only my plumber but several others failed to realise that the hot water system should be depressurised by turning off at he mains and opening a tap to cut the pressure in the pipe; only, then pump up the internal bladder to 2 - 3 bar.
I will give that a try before adding another such expansion vessel.

 

[Harryhound]

Just to give this thread "closure": I persuaded my daughter, who is fair and forty and narrower in the shoulder than I, to operate the valve from inside the corner cupboard.
Meanwhile, I pumped the "Oxford" tyre pump by removing the drawer in the said kitchen cabinet.

Having turned off the mains pressure and released a splash from the hot tap and freed off the valve, I think we managed to correctly repressurise the bladder in the gizmo.

Fingers crossed everything seems to be working correctly and nothing is leaking!

 

[Stigster]

It seems that not only my plumber but several others failed to realise that the hot water system should be depressurised by turning off at he mains and opening a tap to cut the pressure in the pipe; only, then pump up the internal bladder to 2 - 3 bar.
I will give that a try before adding another such expansion vessel.

I still find this problem too and cannot believe that such a basic thing is not understood by trained plumbers. I've spoken to people who have been plumbing for years not realise they need to de-pressurise a system before checking and filling expansion vessels. You just get a false reading on your gauge otherwise and charge to a pressure too low for the vessel to operate correctly.

If you understand what the vessel is doing and how it works that should be obvious really.

I reckon if you do what you yourself have suggested re. the expansion vessel recharge you'll fix the problem.

 

[SJB060685]

I second that Stigster, it baffles me how some so called plumbers don't realise that lol