Vaillant EcoTec 831 pressure issue

[KOTN]

Hi folks

I've researched a fair old bit and followed some advice from other posts and have some findings - not 100% sure what the findings mean though so just looking for a steer before I get a professional on the job.

We have a Vaillant EcoTec 831 combi, 6.5yrs old. Serviced every year, September time.
Always been brilliant, no issues so far...

3 weeks ago woke up one morning and the heating hadn't come on. Trundled off to the garage where it's kept, and a warning was on (I think it was F22 off memory) relating to low pressure. Was at 0.4. I topped it up,probably only the 3rd or 4th time I've ever had to top it up and first issue of this nature.

It fired immediately, all was good, BUT, I've been keeping an eye on the pressure since. Cold (and I mean it's been off for 6hrs+), I noted the pressure 3 weeks ago at 1.3. When heating it goes to about 2.3/2.4.

But since then, over the last 3 weeks it's dropped to 1.2, 1.1 when cold and today down to 1.0. So suspecting a leak of some type I've read up on here.

First off, no known rad leaks. checked and double checked, including visible joints etc.

So I located the PRV outlet pipe and put a container underneath it. Topped up the pressure to 1.2 (cold), and turned the heating on. Went back about 10 mins later and the container was full (approx 200ml, give or take). Had overflowed a little too.

I emptied it, and went back again another 10 mins later and it's got a little more in there, currently boiler still firing to match the thermostat demand, pressure currently 2.3.

Have I located the source of the 'leak'? Would you expect an immediate discharge of water into the PRV pipe (please excuse my lack of correct terminology) straight away? And a decent amount at that?

If so is it likely to be a repressurise type job/diaphragm issue? To be clear those are WAY above my skillset and I'd defo be getting a professional in. Likely to be expensive?

Thanks all.

 

[CWHEATING]

From your explanation,due to the sporadic increase and decrease in pressure it sounds to me like your expansion vessel may need replacing. Probably best to change PRV also. They tend not to seal properly once water has been let through them a few times.

 

[KOTN]

Thanks CWHEATING.

Just for info, after that initial purge that filled the container (approx 90 mins ago), heating still running fine and the container has now perhaps 30/40ml in it, estimate.

Just to fully get my head around it, I take it that NOTHING should be coming out of that pipe if all is well? The pressure certainly won't have exceeded 3bar in the short time it was, hence the assumed fault.

I'm looking at fixed price repairs at present, which with BG for example are based on time taken.

Any idea how long such a repair would take (replacing the expansion vessel and prv as suggested)?

Thanks again.

 

[CWHEATING]

Nothing should be coming out of your pressure relief valve. It is a safety feature on the boiler. When pressure is released in turn the pressure out of your boiler will decrease.
The reason why this is happening is likely to do with a faulty expansion vessel.
When water is heated up it expands. Because you have a sealed system the boiler has an expansion vessel. Inside the expansion vessel is a diaphragm which expands when the water gets hot. The hotter the water the more it expands. (Try turning the temp down on your central heating to reduce water/pressure loss) If the diaphragm has perished then the water has no where to expand causing the boiler pressure to increase above 3 bar and in turn to be let out of the PRV.
If this is the case then it should take no more than an hour or two. The parts should cost no more than £100

 

[KOTN]

Sincerely appreciated CWHEATING, thanks again.

 

[CWHEATING]

If you want to know to know what I’d charge if it was the problem I stated it would be around £300 all in parts&labour

 

[KOTN]

Good to know, thanks again. I do have a boiler cover element to my home insurance but I suspect it's for emergencies only and not this type of matter. Might try my luck on the off chance but otherwise braced for the hit. Could be worse!!

 

[CWHEATING]

Technically there’s no reason you should have to top up your boiler pressure yourself. That’s something done as part of your boilers service. Not everyone is as clued up as you.
It does count as an emergency if you have no heating and hot water which is what you would have if you didnt top the pressure up yourself. Try saying you have no heat or hotwater.

 

[KOTN]

Fair point that, I might embellish it a little and see how I get on.

Haha I'm only 'clued up' from reading on this site. Plus I used to have a Ravenheat in my old house so spent a lot of time watching it get fixed...in fairness it did the job with support from the insurers!!!

 

[CWHEATING]

A Ravenheat to a Vaillant? That’s like trading a Morris Miner for a Rolls Royce

 

[KOTN]

I know hahaha, I moved up in the world!!
Gonna get onto my insurers tomorrow, will let you know outcome. Thanks again.