Boiler pressure drop

rickyroma

We have a combo boiler which is losing pressure. Has to be topped up every week. Was only serviced last month. Would a service pick up on a faulty boiler pressure valve or would this have to be checked separately? 
 All the radiators have been bled and all visible joints checked for leaks. Also, no visible wet patches anywhere in the house. Anything else I can do before I arrange a pricey call out to check the boiler valve? 
It's a 2 year old new build house by the way 

grumbler

I think, if it's the pressure release valve, you will see the water dripping especially when the boiler starts heating CH water.

Mutton_Geoff

Was it losing pressure before the service? Loss of pressure is a leak so those top ups are going somewhere. Better to investigate. At two years old, is there still a warranty in place for the heating system?

Teapot55

A few years back we had the same problem with our combination boiler.  Our gas engineer even tried isolating the feed to the radiator in the downstairs bathroom in case the water leak was under the concrete floor. It wasn’t. 

In the end he rang the manufacturer (Worcester Bosch). They asked for the serial number of the appliance and then informed him that there was a fault in some boilers with cracked heat exchangers. We envisaged a huge bill at that point but they then informed him that it was three years into a five-year guarantee period. The next day they sent a smartly-dressed engineer, who arrived with a new heat exchanger which he replaced in no time at all. All covered by the guarantee. 

(If only the original ‘competitively priced’ bloke who’d installed it three years earlier had told us it had a long guarantee and then not refused to answer our subsequent requests for help we’d have saved even more money and hassle!)

ThisIsWeird

Hi Ricky.
As said by others, check what warranty you have.
Make and model of boiler?
Things to check: two pipes, one 15mm copper and the other 22mm white plastic, should be exiting your boiler, and go through your nearest external wall to the outside. Can you ID these?
Nothing should be coming out the copper pipe. If in doubt, rubber-band a plastic bag over the end.
Water (condensate - so slightly acidic) will be coming out the plastic pipe in glugs, when the boiler is running, but nothing should be coming out when the boiler is cold and has been off for a while.

If water comes out the copper pipe, that means the pressure safety valve has been triggered. You should know that this is an issue by the pressure reading soaring when the CH is turned on. Does it? What pressure do you top up to, and what does it go to as the boiler fully heats up?

If water continues to come out the condensate pipe when the boiler hasn't been run for a couple of hours, then that suggests a cracked mainX.

If neither of these, you can check for a radiator/pipe leak by repressurising to the normal 1bar, turning the boiler off at its power supply, and closing the CH flow and return valves under the boiler. This will isolate the boiler from the rad system. If the pressure still falls, the loss is within the boiler. If the pressure falls when you reopen the valves, the leak is in your rad system and pipes.

If the issue didn't exist when the boiler was serviced, the guy wouldn't have known about it. 
And I can't think of any he could have done to cause it, other than perhaps topping up the pressure carelessly, and exceeding 3 bar; once these valves are popped open, they don't tend to reseal very well.

rickyroma

I noticed the pressure was about 0.5 the morning before the service. Not something I religiously check until now. 
I remember at the end of the service he asked me to turn on the heating so I assume he was checking the valve then? 
 Thanks for all the advice, plenty to think about! 

ThisIsWeird

You don't 'check' the valve, normally. I doubt most would even look at the pipes outside. 
If they suspected summat was amiss - like a low pressure - then I'd like to think they'd ask you about this, to see if it is an issue, or just a quite normal gradual drop.
So, what happens with the pressure? What does it start at cold, and what does it go up to?
And, worth a look at the outside pipes?

rickyroma

If there is any air in the system would this cause a drop in pressure?  I mean, is 100% water going to maintain pressure better than if air has got in there?  Just wondering if it's worth double checking the bleeding of the radiators to completely rule this out? 

ThisIsWeird

rickyroma said:

If there is any air in the system would this cause a drop in pressure?  I mean, is 100% water going to maintain pressure better than if air has got in there?  Just wondering if it's worth double checking the bleeding of the radiators to completely rule this out? 

As you have surmised, 100% water in a sealed system will cause problems! Water expands with heat, and the pressure would soar. That is why you have an EV (expansion vessel) which is half-full of air, separated from the water by a rubber diaphragm. As the hot water expands, it compresses the rubber against the air side, and the EV takes in the expanded water. When the system cools, the water contracts, and the air bubble returns to normal - ergo the pressure remains pretty constant.

So, if your pressure IS soaring, then it's almost certainly the EV.

A large amount of air in a radiator would actually act like an EV, and help keep the pressure stable!

But, a large amount of air in a rad could also indicate that the EV rubber has punctured, allowing the EV's air into the water.

So, yes, by all means check your rads for air.

But please also feed back on the other stuff I pointed out - they are all big clues.

grumbler

ThisIsWeird said:

rickyroma said:

If there is any air in the system would this cause a drop in pressure?  I mean, is 100% water going to maintain pressure better than if air has got in there?  Just wondering if it's worth double checking the bleeding of the radiators to completely rule this out? 

As you have surmised, 100% water in a sealed system will cause problems! Water expands with heat, and the pressure would soar. That is why you have an EV (expansion vessel) which is half-full of air, separated from the water by a rubber diaphragm. As the hot water expands, it compresses the rubber against the air side, and the EV takes in the expanded water. When the system cools, the water contracts, and the air bubble returns to normal - ergo the pressure remains pretty constant.
...
A large amount of air in a radiator would actually act like an EV, and help keep the pressure stable!

IF the system was refilled and IF there was some air in the system, then theoretically it can dissolve gradually in the water under pressure and cause a drop in pressure.

sevenhills

We are having water pressure issues with an elderly relative Ideal boiler. The water has been topped up five times now. Most recently the boiler man maybe put some sealer? in the system. We weren't there, so unsure.

I topped to water up yesterday, it went a little too high, so it was 2 3/4

When I looked today, after the boiler man had been, the pressure was at 1, there is a rusty radiator in the downstairs toilet, that was always turned off, but in recent months it was turned on.

The boiler man thought it could be the expansion tank, but there was no water leaking/dripping outside.