On Sunday, 24 November 2019 12:56:23 UTC, Lee Nowell wrote:
On Sunday, 24 November 2019 12:27:50 UTC, Dave Liquorice wrote:
On Sun, 24 Nov 2019 02:32:41 -0800 (PST), Lee Nowell wrote:

2. It is because the expansion vessels have run out of air. I appear to
have 2. One in the inbound supply side and one on the circuit coming out
of the boilers. Some people seem to say to just check them and if low
too them up (not sure to what) with a tyre inflator (presume the little
compressor thing I use to pump tyres up). Others say this is very
dangerous. Also TBH not sure what the purpose of either is and therefore
which one is likely to be it

Water expands when heated, the expansion vessels give some where for
this increase in volume to go. They are simply a chamber with a
stretchy membrane across with the water one side and trapped air the
other.

If safe, I could do both of course.

You have two as the boiler circuit is seperate to the domestic HW.
Both being sealed both need expansion vessels. As we are looking at
the HW side then it's only the expansion vessel on that we need to
worry about. If it has failed then the pressure can get *very* high
and this could force water out of places it shouldn't come out of,
like that pressure reducing valve.

The vessel should have car tyre like valve press the little bobble in
the middle air should hiss out, no wet. If wet the vessel has failed
and needs replacing. Not 100% fool proof if the valve isn't at the
bottom but they normally are... If dry it may of lost pressure on the
air side but this isn't the normal failure mode. To repressurise I
think you'd need to de-pressure the wet side and pump up the air side
to a preset value dependant on that particular vessel, that figure
might be on the label.

--
Cheers
Dave.

Thanks all. Seems like getting the actual part number has aided my googling... Looks like other have has the exact same issue and taking out the assembly and cleaning it seems to have sorted the problem for some. It is referred to as "cleaning the strainer". Will give this a go next weekend.

In response to the other questions...
1. yes mine has a car tyre type valve at the top will try and get a reading on it
2. no water coming out of the tundish

Couple of follow up questions
1. The valve has an adjuster on it. If I turn it up I assume I will get greater water pressure in the house (assuming it is limiting it)? The showers a ok but could be better - I had always assumed it was the inbound pressure being the issue.
2. I have recently had problems with an existing thermostatic shower where the hot seems to have "suddenly" over take the cold pressure and it is not getting much colder when you turn it down. Similarly, as new one I fitted a few weeks ago had the opposite problem where the cold was overtaking the hot and I had to adjust (a lot) the cold flow at the shower to make it work. Wonder if these are symptoms relating to the current issue discussed above?

thanks

Lee.

So just checked the expansion vessels.... The one on the boiler side had air in it although unfortunately the valve was sticky to stuck open when I tested it so a fair amount of air came out. Now sitting at 1.1 bar according to one of the car tyre pressure gauges that pop out an inner cylinder to read the pressure (not sure how accurate they are).

The expansion vessel on the cold feed side nothing comes out at all. Looks like that needs filling?