A freind has had the on call plumber out repeatedly lately due to low water pressure on the boiler,the boiler reapeatedly needs topping up,no evident leaks are visible.

They just refill thew boiler and on there way they go.

How much water does a boiler hold, and any reason for loss of water pressure.

There will be a leak somewhere. Check all the radiator connections to the pipes for weeping.
Just to cheer you up the cause of the pressure loss in our combi boiler was a split in the pressure vessel

Is there any water dripping from it’s overflow pipes ?

Top up the pressure, knock off the heating & close the flow & return stopcocks. Monitor the pressure for a while. Would possibly indicate if the leak is at the boiler…

This aside, they need to insist the system is fixed properly.

Over pressure valve is a VERY common one- leaks to the drain so you never know

Probably needs a new expansion vessel, if it’s covered by a contract, I’d be asking for one.

Then get any old rads replaced.

housing assosiation rental property, and they dont seem intrested.

Find out where the blow off valve pipe is, usually a 15mm pipe through the wall, zip tues a plastic bag to the end.
If yiu go back a day later and see water inside will be a faulty pressure relief valve
If its not that the diaphram on the vessell could be ruptured, so when the water gets hot and expands, its nowhere to go, and lifts the pressure relief valve
If its a faulty valve they usually drip, if its a faulty diaphram, it will be more sudden

Either the pressure release valve has gone or the expansion vessel has gone – the former is a lot cheaper than the latter.

If its a rental yiu dont need to worry 🙂

Can they not monitor the pressure and top up the system themselves when required, rather than calling a plumber and waiting for them to come and sort it ?

It’s hardly a complicated task, and it would save them a lot of hassle.

What they said.

My expansion vessel pressure got low and blew the prv . Was told it would likely need a new prv ( in a phone call to my uncle the heating engineer)) and low and behold i need a new prv…. Once triggered they tend to fire lower and lower…..on my boiler anyway. Now it fires at 1.5 bar instead of 2.5 bar…. Although if any heating engineers want to contest that im all ears.

Tell them to open the filling loop for about 5 minutes then shut if off. That should cock something up royally enough for them to actually get it fixed. Usually housing associations are pretty good when it comes to repairs.

Can they not monitor the pressure and top up the system themselves when required, rather than calling a plumber and waiting for them to come and sort it ?

It’s hardly a complicated task, and it would save them a lot of hassle

No ,due a disability and being in a wheelchair and not being able to reach it.

When it reaches a low presure it cuts out so no heating or hot water,not nice if youre in a wheelchair.

If its a condensing boiler, it could also be the main heat exchanger and water disappearing down the condensate drain. But if its a housing association property there is not really much you can do.

If nothing leaking or dripping.then it willdefo be the the fill up valve not shutting or sealing off proply then the water in system leaking backwards through the fill up loopy thing. not a plumber and drunk.

“If nothing leaking or dripping.then it willdefo be the the fill up valve not shutting or sealing off proply then the water in system leaking backwards through the fill up loopy thing. not a plumber and drunk.”

Good job you added that last bit because its about as definantly that as my walls are definantly green* it might be that but i doubt it.

* they are magnolia.

Yep trail rat “defo” the wrong word but always look at the simple solution first although I would bow to your expertise you using acronyms concerning the combi boiler field an all.

As above, we had the valve blow and it was going undetected for months before BG finally sent someone with more than two braincells.

We’ve also had a slow pipe leak but because it was leaking out slowly over plasterboard, it dried out fast enough not to be noticed for ages.

I think Trail Rat is right about the fill loop:-

Aren’t fill loops a removable key or flexi hose and ALWAYS had to be disconnected after fill??? I thought WRAS reg was there deliberately so there was no chance nasty heating water could back fill the drinking supply? Also, the mains water is higher pressure than the heating circuit, so how could it ever leak that way?

My money is on pressure relief valve, possibly but not always related to pressure vessel failure (mine weeped just by using it to remove pressure to work on a rad without ever “going off” due to over pressure). Or a small leak somewhere else – it must only be a weep somewhere as it obviously holds pressure when they refill the thing. Not a lot of water loss is required to drop the pressure (just the amount used to move the diaphragm in the pressure vessel plus compress any air in the system).

if pipes run under floorboards leak may be missed.would like to think if it was the prv even the thickest of plumbers would find that