Boiler pressure dropping - should I open the valves?

united4ever

Btw the pressure back up to 1 now son has finished shower so yes the system is working to some degree.

Hudsonbutler

Maybe the other EV has gone. Just had both of mine replaced and the PRV.

Bendy_House

united4ever said:

Btw the pressure back up to 1 now son has finished shower so yes the system is working to some degree.

Both of these valves need to be opened before water can flow to repressurise the system, so you should be able to open just one without anything happening. The top valve looks slightly easier to control - it has a slightly larger handle - so that's why I suggested opening the bottom one first - and nothing should happen - and then slowly tweaking the top one open, very slowly, and stopping as soon as you hear the hiss of water. If it's hard to control, then perhaps slipping a spanner or something over the handle to give it extra control might help?

It does sound, tho', as tho' the amounts of water being lost are small, so perhaps there isn't a significant leak, but just a drip somewhere.

Good, you are familiar with what was happening before with the pressure - it was obviously increasing to the point the PRV was forced open, and this dumped some of the system water out that copper pipe. You now need to check that pipe again, just in case. (Small freezer bag, rubber band...)

Unusual behaviour from your pressure now, tho'. You say that when the shower was run, the pressure dropped? And as soon as the shower ended, it went back up? That's weird.

Ok, what did it drop to when the shower was used? And did it jump up immediately when the shower was ended, or did it take a while? Have to say, I haven't a clue what's going on there... :-(  

Bottom line - your pressure should be fairly steady throughout; around 1bar or slightly more when the system is cold or off, going up by, say, a half-bar when running hot. But no real concern unless it starts going over 2bar.

Double-bottom-line - if your system is losing pressure, you need your plumber out again. It needs to be sorted. And I'd also ask him to check the 'inhibitor' level in your system, because every time you lose some water and top it up again with 'fresh', the inhibitor level becomes a little more diluted. Not good for the health of your system.

I see you have a magnetic filter fitted - that's very good. When was that last checked, and was there much 'stuff' inside it?

united4ever

Thanks. When my son was in shower it dropped to just a whisker over 0. It was ten minutes later I checked and it was back up to just over 1. I will check more closely how long it takes to get back up tonight.

One discovery today is to do with towel rail in bathroom which has one valve. I generally keep it turned off all the time. However, it seems that turning it on makes the pressure go back to and stay at normal. Some web research reveals this is not uncommon. I was told by boiler man that at least  one valve should be fully open all the time. So I kept the living room one fully open. Seems like this towel rail may also need to be on. If so, I don't really want to heat the bathroom all day every day. It will cost more to heat but maybe I am overly frugal. Not sure if the towel rail is a red herring or not but seems to work so far.

Great advice upthread. It's an education for me!

Bendy_House

It is usually recommended, especially for boilers that do not have a built-in 'by-pass', for one rad to act as this by-pass. It allows the water to circulate even if the other rads are fully shut off, as they may do via their TRVs closing down. It isn't good for a boiler to have a fully restricted flow as it cannot then get rid of the heated water inside it. Cue lots of rumblings...

I really don't know what's going on with your pressure when a shower is taking place and then afterwards; that doesn't follow a normal pattern to me. There could be some obvious reasons such as, when the shower is running, then only a small amount of the system water is being heated inside the boiler - it goes around and around - and therefore there isn't much water actually 'expanding' to cause a pressure rise. However, once the shower (DHW draw) stops, the CH comes back on, and now you are heating 100's of litres of radiator water, so expansion will take place = rise in pressure.

Coming back to the bottom line - your pressure should not be dropping as a rule, and you should not be needing to top up your boiler pressure more than, say, once or twice a year.