Combi Pressure relief valve pipework. Do not use!

[cropston]

Yesterday, following an annual inspection, a BG man hung a notice on my mother's combi boiler saying "... in the interests of safety do not use until any faults have been remedied." The "fault" in question appears to be that the pipe from the pressure relief valve is routed upwards into the loft space above the boiler before (I assume) it goes outside somewhere. The boiler was installed in 2007 and was inspected a year ago without fault. I could not find anything in the Worcester installation guide from 2007 regarding the routing of the PR pipe although there is a mention in the 2010 guide. The general advice seems to be that the PR pipe should be routed downwards from the boiler to terminate somewhere safely. Is the fact that the pipe goes upwards sufficient justification to hang a sign on the boiler to say that "it should NOT be used". I think that any warning, if warranted, should be couched in terms of saying that it is not in accordance with current or good practice and that it would be ADVISABLE to make changes. Has the guidance changed since 2007 or are some inspectors being far too cautious in hanging a scary sign on a boiler that doesn't need one?

 

[cross thread]

BG say a pressure relief pipe that does not terminate safely is AT RISK but they cannot turn the appliance off whithout owners permission,i suspect he is covering his own ass,if the pipe is discharging safely then it is not to the new standards,and recorded as that

 

[kirkgas]

if it goes vertically up into a cold (potentially frozen in winter) then any water in the pipe in the loft will freeze and stop the near boiling high pressure water escaping to outside and could cause serious injury/damage so i would have stuck a warning label on it as well

 

[cropston]

if the pipe is discharging safely then it is not to the new standards,and recorded as that

Presumably you meant to say "is not discharging safely" rather than "is discharging safely." I don't know whether he checked to see whether it was discharging safely or just noted that it was going up.

 

[cropston]

if it goes vertically up into a cold (potentially frozen in winter) then any water in the pipe in the loft will freeze

If the pipe in the loft slopes down to its discharge point I can't see how it would have any water in it to freeze. However, I don't know whether he checked this.

i would have stuck a warning label on it as well

Is there not a label that gives a warning rather than says "do not use"? The valve might go off but it seems unlikely that anyone would stop using a boiler altogether with temperatures below freezing for what I suggest is a very low risk and which could be attended to when things warm up a bit.

Notwithstanding this, I would like to know if there were any regs that existed in 2007 which stated that this was not the way to do it in which case I will insist that the installer must sort it out. If the regs have changed subsequently then he might just have some sort of excuse.

 

[Agile]

Is there not a label that gives a warning rather than says "do not use"? The valve might go off but it seems unlikely that anyone would stop using a boiler altogether with temperatures below freezing for what I suggest is a very low risk and which could be attended to when things warm up a bit.

Notwithstanding this, I would like to know if there were any regs that existed in 2007 which stated that this was not the way to do it in which case I will insist that the installer must sort it out. If the regs have changed subsequently then he might just have some sort of excuse.

Its not up to you to write gas regulations ( unless you have been appointed to the Standards Setting Committee ). Not do I think that you have the necessary understanding and experience based on what you have said above about it being "a very low risk"!

Surely if its such a low risk as you suggest, then I would not have seen a boiler which exploded as a result of a frozen PRV vent last month.

I am not aware of any new regulations in this respect since 2007 but I could have missed out on one. If you just speculate on this because no one commented previously then perhaps they just failed to notice it?

There are also internal instructions within BG which are based on company policy and is placed after consideration of risk factors.

To anyone experienced with boiler installations the risk is obvious. Even sloping down in the loft is not sufficient as the PRV may be leaking slightly and the resulting flow freezes and blocks the pipe regardless of the slope.

Tony

 

[doitall]

It doesn't come under gas regulations, it's in one of the BS documents. Wras approved design whatever.

The more the pipe rises the greater the pressure would be needed to blow off.

In addition the water in the pipe can cause corrosion, sludge and any number of unknown blockages, including freezing.

However according to a discussion I was having the other day, a pressure relief valve is not consider a safety device anymore, when limits stats are fitted. (I don't agree)

 

[Agile]

Whatever discussions you have in the pub or even the church next door, its common sense that a PRV is a useful safety device to protect a boiler from excessive internal pressure. That can arise from over temperature OR over pressurisation from the mains wate via the filling device.

Most people probably take the view that the PRV should be fitted at the boiler and only the discharge taken upwards. In that case when its not letting by the pipe will be dry.

Tony

 

[doitall]

Whatever discussions you have in the pub or even the church next door, its common sense that a PRV is a useful safety device to protect a boiler from excessive internal pressure. That can arise from over temperature OR over pressurisation from the mains wate via the filling device.

Most people probably take the view that the PRV should be fitted at the boiler and only the discharge taken upwards. In that case when its not letting by the pipe will be dry.

Tony

College teacher actually Tony, you may have read it.

I have wondered what the implications would be if you done away with the PRV on the boiler, and either fitted a second one in the flow at high level so you had the required fall, or extended the fitting in the boiler to high level, and re-positioned the prv higher.

The PRV would still be on the system side, and you could meet the regs, regarding the correct falls.

 

[Agile]

Another thread suggested at least one manufacturer recommended that a PRV is fitted on the floor above so it could discharge downwards if the boiler is fitted in a cellar with no where to safely discharge.

Tony

 

[cropston]

I fully appreciate the need for a PRV and the need for the pipework from it to be able to resist steam. No one has commented on what appears to be the lack of any reference in the MI at the time to PRV pipework or to any changes that have occurred subsequently.

Is there not a label that gives a warning rather than says "do not use"?

Its not up to you to write gas regulations

I was only asking if a warning sign which did not include the words "do not use" existed -presumably it doesn't. The low probability of the PRV going off would have to be multiplied by the low probability of the pipe freezing up so the risk is going to be very small. That is not to say it will be zero but turning the boiler off on an old lady in freezing conditions, is I would suggest, a far bigger risk.

The more the pipe rises the greater the pressure would be needed to blow off.

2m rise is < 0.25bar compared to PRV which blows off at 3bar, so not that significant.

one manufacturer recommended that a PRV is fitted on the floor above

This seems to suggest that the fact that the pipe goes up is not important. The problem is to do with whether it gets blocked up after the valve.

Most people probably take the view that the PRV should be fitted at the boiler and only the discharge taken upwards. In that case when its not letting by the pipe will be dry.

The boiler is designed with an integral PRV. The vertical pipe might not be dry if the valve has leaked at some time. The vertical pipe will definitely be full of water if the PRV is placed at the top. I can't see why the PRV pipe is going to suffer from corrosion or sludge any more than any other pipe in the system and the only blockage risk seems to be freezing. If this is the case, why not use heat resistant insulation.