Ravenheat Condensing Combi Playing Up

[Rob_the_rich]

reading the instructions for that boiler, they are pretty good at showing the size of expansion vessel needed compared to system volume. They do say to subtract the existing one, but you can ignore that. They also say that the replacement of the existing one cannot be done without taking the boiler off the wall. So what you are looking at is the best option, don't forget to get a bracket if one is not supplied.

Edit; don't forget to add some inhibitor to the system, yours will be well diluted by now, if there was any in the first place

 

[revjames]

reading the instructions for that boiler, they are pretty good at showing the size of expansion vessel needed compared to system volume. They do say to subtract the existing one, but you can ignore that. They also say that the replacement of the existing one cannot be done without taking the boiler off the wall. So what you are looking at is the best option, don't forget to get a bracket if one is not supplied.

Edit; don't forget to add some inhibitor to the system, yours will be well diluted by now, if there was any in the first place

Come to think of it the water was clear not black like I expected

 

[Rob_the_rich]

Come to think of it the water was clear not black like I expected

Does not mean that it is not black in the radiators. Might also be that it has been flushed continuously by the inlet valve that was letting-by and being expelled by the PRV.

Every time the system is filled with fresh water, any inhibitor is diluted AND dissolved oxygen in the water is introduced leading to rust. Best to add some inhibitor, a good place is usually the towel rail since the bleed valve is on the top and can be unscrewed easily (edit; with a spanner, the whole valve) for pouring when drained down a bit.

 

[revjames]

do you think the inlet valve passing contributed to the failure of the expansion vessel?

 

[Sharpend]

Difficult to say to be fair, if it was significantly in breach then quite possibly, if it was trickling through then doubtful.

On a side note, I always thought boilers had a Pressure Release Valve to prevent over pressurisation? Thought that these blew at about 3bar?

 

[Rob_the_rich]

do you think the inlet valve passing contributed to the failure of the expansion vessel?

No, under normal use any pressure spike on the mains should open the PRV. Most mains pressures aren't up to 3bar anyway. Although the instructions do say that oxygen and other gases might contribute to the rubber failing, that is why they use just nitrogen in the pre-charge gas (inert)

The diapragms occasionally just split, and I think that is what happened.

It does worry me that your PRV opens at 4bar, maybe look to replacing that too while you are at it. The PRV does make an excellent way of draining the boiler by the way, just turn the red knob until just before it clicks shut (some PRVs have levers, and some you can't open manually). Not recommended to use it to drain the boiler usually, since dirt/particles can get between the seating of the valve and it can drip, but if you are going to replace it, you might as well use it. It is basically a spring holding a washer to the seating.

 

[Phoenix]

I presumed the PRV was a one time device and and required replacing if activated. Pictured it as a rubber membrane in a section of tube which broke if pressure was too high?

 

[Rob_the_rich]

I presumed the PRV was a one time device and and required replacing if activated. Pictured it as a rubber membrane in a section of tube which broke if pressure was too high?

No not usually in combis. Some servicing instructions require an engineer to open the PRV. But as mentioned above it sometimes means that it does not close again fully and even after loads of opening and closing it still drips and needs replacing or a thorough cleaning when taken off of the boiler.

 

[revjames]

THE PRV does operate at around the 3 bar point. Interestingly, Just been away for 4 days. Before I went, I pumped up the EV to 0.5 bar and ran the CH. Pressure went up fairly quickly and PRV operated. Went to top rad in attic bedroom and it was full of air.... Bled some out while I was there but hardly any water pressure in system so did not bleed fully.

Just back home and house cold so, filled system to 0.5 bar and ran system. Worked fine with pressure staying at around 2 bar. My theory is the top rad is half full of air and is acting as a EV. Redneck fix?

I can leave it for a while and summer time I will fit the EV, drain system and fit TRVs on all the rads (been meaning to do that for ages)

 

[Rob_the_rich]

Yep, redneck fix.

Do you have a room thermostat? If so, don't fit a TRV in the same room as the roomstat, they interfere with each other. If no roomstat, best to not fit a TRV in the room (hall or lounge) where you intend to put one. The MI for the boiler might specify a minimum flow or a system by-pass, I didn't check. Roomstats are worth fitting, they repay themselves pretty quick since can cut 10% off gas bill.

 

[Sharpend]

That would explain the symtoms that you have had. Would just monitor pressure when cold to see if it drops as could be a slight leak within system.

Also wouldn't waste money on TRV's, ok for first couple of years then the valves stick and before long they need to be replaced.

 

[revjames]

sorry to be back on this and thanks in advance for helpful replies. I recently fitted EV - a separate one. CH was working OK for a week or 2. Pressure was low so I needed to top it up, no water entering system, at least no increase on pressure gauge, Manually operated PRV and reading on gauge did not change. Replaced check valve and water IS now entering system via filling loop but reading on gauge static. - Unless it wont go above 1.5 bar because of EV - which is larger than the original?

Anyway the problem I now have is the red light (overheat/ flame failure) comes on after about 10 seconds and no sign of any sparks to ignite burner when heat is called for. Really getting peed off with this boiler now!