It was so full that it was leaking water under it, so emptied it out, there is a mark about 1cm high on it marked service level. Should I refill it to water at this level?
I think the service mark shows when to clean out the sump - if debris is over the line it should be cleaned out. According to most manufacturer’s instructions, the trap should be partly filled before refitting as it will stop flue gases getting through. In practice the trap will refill itself within half an hour or so if the boiler is working. Are you able to blow down the pipe (usually plastic) that leads away from the trap, or pour water down it, to confirm that it isn’t blocked?
Thanks just went to check in a panic as you mentioned dangerous gases, so I guess carbon monoxide, the sump seems to refilled itself 1/2cm over the service level mark. I wish it said in the manual that it had to be refilled with water, not just emptied!
Once the condense water gets to a certain level it should automatically drain itself, leaving enough to still create a trap. If yours is effectively overflowing and leaking then it’s likely that the route it takes to drain away is blocked. Often, the condense pipework is joined to a flexible hose under the boiler and you may be able to disconnect here and either blow or pour water down to check that it’s clear.
Boiler needs a service though, all the sediment and particles in the trap have came from inside the burner
Took a pressure reading with gauge and it was 2.2 bar, same reading as on boiler. So pressed the Shrader valve pin to let out air, but then water came out! Was I suppose to bleed the radiators before taking a reading?
Your expansion vessel has failed and needs to be replaced. The diaphragm has perforated, which is not uncommon. Just bite the bullet and get a new one. They're not that expensive, but try to get a good one, e.g. Zilmet. Don't be fooled into getting the one sold by your boiler manufacturer, as they just apply a massive mark-up. I recently bought a brand new Zilmet one for £10 on eBay from a heating engineer who was retiring. The identical one for my Grant UK boiler from Grant would have cost well over £100.
Thanks for the prompt reply! Will an external expansion vessel be cheaper to fit? Could it be the extra radiator that was fitted that has blown up the expansion vessel?
I think you'll find the expansion vessel had failed before you fitted the additional radiator and that one of the radiators had a quantity of air in it thus acting as your expansion vessel. In fitting the new radiator you refilled the system and bled all the radiators thus releasing the air that was trapped in a rad and acting as the expansion vessel. Just had exactly that problem on my daughters system. Dad, can you just....
External expansion vessels have the huge advantage of not being constrained by the small size requirements of fitting inside a boiler housing. You can't have an expansion vessel that's too big, but you certainly can have one that's too small. If you have the room for an external one, go for something nice and big like a 25 litre one. My standard internal one is 14 litres, but I added another one externally to give me another 10 litres, so I will hopefully not be going through them at the rate I used to. Mind you, I think my 14 litre internal ones were failing as much because they were getting too hot (being so close to the actual furnace of the boiler) as because they were probably marginal in size. Time will tell.
Can we use a self cutting isolating valve to install an external expansion vessel on the return flow pipe?
I would say no. You can't have an islolation valve on the pipe to a vessel. It could accidentally be turned off.
That's great news. But you would need a screwdriver to close it, maybe easier to change too if faulty. https://www.screwfix.com/p/self-cut...gclsrc=aw.ds&dclid=CLn8k_7n5NsCFYqmUQodw2IJdw
To be honest, replacing the current vessel is probably the best option. It's really simple to change and with only 8 rads it should be up to the job.