Worcester boiler low pressure

330d

I have a Worcester system boiler and about twice a year it goes to low pressure.

But when I top it up, it jumps to 0.2bar to 1.2-1.4 bar within a second. To me this is very strange as in my previous house it used to take a few seconds to top the boiler, not a split second.

Do you think the boiler was actually low on pressure? If so, is it normal to build pressure within a second?

Also after I do this, it shows two flashing squares meaning it's in a air purge mode.

https://www.worcester-bosch.co.uk/support/troubleshooting/faqs/all-faqs/what-do-the-error-symbols-mean-on-my-boiler

ThisIsWeird

Could we have a pic of the filling method, please.
Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first inserted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.
Can you hear the water flow as you top it up? It should be obvious whether it's hissing in slowly, or roaring too fast?
Bottom line, tho', is that your boiler will almost certainly just stop working completely if the pressure falls too low, so since there is summat amiss with the pressure gauge, I'd be inclined to let this happen before topping up again - I wonder if it will?!
Does your boiler also have a digital pressure reading (assuming the one you are referring to is analogue)? If so, do the values correspond?
What's happening here? No idea, but a faulty gauge (analogue) or pressure sensor (digital) must be suspect.
When you top up, do you first shut the boiler down completely? If so, that start-up symbol could be a condensate trap refill sequence - have a look at the instructions. 
You don't need to shut the boiler fully down, but just remove any calls for heat so it isn't running.
Once it's topped up and running again, is the typical 1.2bar pressure quite stable as the boiler heats up? With the CH nicely hot, what pressure is it at?

Albermarle

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

330d

Albermarle said:

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

Ok interesting, seems topping the boiler up every 6 months is to be expected 

ThisIsWeird

330d said:

Albermarle said:

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

Ok interesting, seems topping the boiler up every 6 months is to be expected 

Yes and no. Wee top-ups are ok, but significant pressure loses aren't good.

Yours is weird - it seems to indicate a largish loss, but it refills super-quick, so that indicates no great loss at all.

Does your boiler also have a digital pressure gauge? If so, does it agree with the analogue one?

330d

ThisIsWeird said:

330d said:

Albermarle said:

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

Ok interesting, seems topping the boiler up every 6 months is to be expected 

Yes and no. Wee top-ups are ok, but significant pressure loses aren't good.

Yours is weird - it seems to indicate a largish loss, but it refills super-quick, so that indicates no great loss at all.

Does your boiler also have a digital pressure gauge? If so, does it agree with the analogue one?

It has both, the analogue one is behind the cover so will check next time if it aligned to the digital one.

And yes it was large loss as the boiler stopped working as it was reading 0.2bar. 

Albermarle

330d said:

Albermarle said:

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

Ok interesting, seems topping the boiler up every 6 months is to be expected 

However in my case I would be say topping up from 1.2 bar to 1.5 bar. 

Rust81

330d said:

ThisIsWeird said:

330d said:

Albermarle said:

Did mil's WB only last week - it just needed a tweak. This one has a large black key that's first I sorted, and then a wee black square block that gets turned to do the actual filling.
No, it shouldn't jump up, so something is amiss. Even if you open the tap too far, the needle will still rise smoothly, and take a few seconds.

As a WB owner, I can confirm the above. Luckily it only loses pressure very slowly, so I only top up every 6 months or so and it does take a few seconds even with the little black tap fully open.

Ok interesting, seems topping the boiler up every 6 months is to be expected 

Yes and no. Wee top-ups are ok, but significant pressure loses aren't good.

Yours is weird - it seems to indicate a largish loss, but it refills super-quick, so that indicates no great loss at all.

Does your boiler also have a digital pressure gauge? If so, does it agree with the analogue one?

It has both, the analogue one is behind the cover so will check next time if it aligned to the digital one.

And yes it was large loss as the boiler stopped working as it was reading 0.2bar. 

I have the same boiler and have had a similar experience over the past few days. The analogue reading is different to that on the digital display. 

This all started when one morning the digital display was showing 0.3 and I had no heating. I repressurised the boiler and it shot up to 2.1 quite quickly which surprised me, then it went through the air purge cycle before the boiler fired up and the pressure dropped back down to 1.7. The digital pressure reading is still showing a higher reading than the analogue reading, so I’ll need to get an engineer out after Christmas to take a look.
 
I’m now keeping an eye on it and have isolated one zone to see if I have a leak on the radiator zone

ThisIsWeird

If the analogue reading doesn't actually move, then it could be a blocked capillary pipe that feeds it. Possibly it could also show as a very slowly responding needle, both up and down; do the pressures match after, say, an hour?
If both gauges actually change readings quickly as they should, then it's lottery as to which one is reading wrong! Obvs only the digital one will tell the boiler to stop working.
If the pressure increases quickly with seemingly little water added, then I think that suggests the Expansion Vessel is full of water, so has no capacity to absorb any more. Perhaps it's kaput, or maybe it just needs an air recharge. Pressing the 'pin' in the Schrader valve can give a good indication - if air or now't comes out, then a recharge might sort it. If water comes out, it's kaput.
Anyhoo, to keep your boiler running, just top it up enough to fire up, and not more. One bar is fine. Keep an eye on it as the boiler heats up - if the pressure initially rises significantly Ie to well over 2 bar - then it's EV.
How are you isolating a circuit? Don't forget it's connected at two ends.

Rust81

ThisIsWeird said:

If the analogue reading doesn't actually move, then it could be a blocked capillary pipe that feeds it. Possibly it could also show as a very slowly responding needle, both up and down; do the pressures match after, say, an hour?
If both gauges actually change readings quickly as they should, then it's lottery as to which one is reading wrong! Obvs only the digital one will tell the boiler to stop working.
If the pressure increases quickly with seemingly little water added, then I think that suggests the Expansion Vessel is full of water, so has no capacity to absorb any more. Perhaps it's kaput, or maybe it just needs an air recharge. Pressing the 'pin' in the Schrader valve can give a good indication - if air or now't comes out, then a recharge might sort it. If water comes out, it's kaput.
Anyhoo, to keep your boiler running, just top it up enough to fire up, and not more. One bar is fine. Keep an eye on it as the boiler heats up - if the pressure initially rises significantly Ie to well over 2 bar - then it's EV.
How are you isolating a circuit? Don't forget it's connected at two ends.

The analogue dial doesn’t seem to move as quickly as the digital reading and I’ve also noticed that that digital reading goes up quickly when the boiler is firing up (not from cold) - say from 1.7 to 2.1 bar within 30 seconds. 

I’ve isolated the UFH zone on both the flow and return into the manifold and that hasn’t had any drop from 2.5 bar. 

Boiler has been ok since the 23rd with no pressure drop. Have put a bag over the PRV and no water collected so far, which I would have thought would have happened if the expansion vessel was full. 

ThisIsWeird

Rust81 said:

ThisIsWeird said:

If the analogue reading doesn't actually move, then it could be a blocked capillary pipe that feeds it. Possibly it could also show as a very slowly responding needle, both up and down; do the pressures match after, say, an hour?
If both gauges actually change readings quickly as they should, then it's lottery as to which one is reading wrong! Obvs only the digital one will tell the boiler to stop working.
If the pressure increases quickly with seemingly little water added, then I think that suggests the Expansion Vessel is full of water, so has no capacity to absorb any more. Perhaps it's kaput, or maybe it just needs an air recharge. Pressing the 'pin' in the Schrader valve can give a good indication - if air or now't comes out, then a recharge might sort it. If water comes out, it's kaput.
Anyhoo, to keep your boiler running, just top it up enough to fire up, and not more. One bar is fine. Keep an eye on it as the boiler heats up - if the pressure initially rises significantly Ie to well over 2 bar - then it's EV.
How are you isolating a circuit? Don't forget it's connected at two ends.

The analogue dial doesn’t seem to move as quickly as the digital reading and I’ve also noticed that that digital reading goes up quickly when the boiler is firing up (not from cold) - say from 1.7 to 2.1 bar within 30 seconds. 

I’ve isolated the UFH zone on both the flow and return into the manifold and that hasn’t had any drop from 2.5 bar. 

Boiler has been ok since the 23rd with no pressure drop. Have put a bag over the PRV and no water collected so far, which I would have thought would have happened if the expansion vessel was full. 

These sorts of figures are in the 'uncertain' territory, and don't point concisely to a cause.
Going over 2 bar is generally to be avoided, tho' - it just isn't necessary, and only places extra strain on the system.
It would be good to know how much the pressure increases from cold, or near as. When the CH has been off for an hour or so. Then monitor what happens as it's turned back on.
Your UFH seems ok - phew!
Keep monitoring it, keep the cold pressure at 1 or slightly above, keep the bag over the discharge pipe.
Let us know what happens.