Combi Issue

[gollancz]

Boiler: Vaillant Ecotec 837 condensing boiler

Just had the above boiler installed and I have a slight problem. Every time I turn on a COLD water tap and then turn it off, the boiler pump comes on for 15-20 secs. This happens every time cold water is drawn from the mains.....i.e. toilet filling, washing machine. As I say, the pump comes on the moment that you turn off the cold tap.

My installer says "read your instructions. This is normal behaviour". But the instructions say nothing about this and having owned a few combis, I have never seen this before. So I don't really believe him.

Can anyone confirm
1) whether this is normal behaviour for this boiler?
2) if not, what might be causing it so that I can tell my installer what might be wrong

Thx
P

 

[DP]

It is not normal behaviour. It is a plumbing issue. Deadleg to be precise.

 

[gas4you]

Exactly as DP says. Your installer has left a dead leg, probably on the old hot supply pipe that used to come from the hot water cylinder.

Get him back to do his job properly.

It is definitely not normal boiler behaviour Was he corgi registered? Did he increase the size of your gas supply for this combi, unless it sits nearly over the gas meter you often have to use 28mm up until the last 6M or so from the boiler.

Did he set it up/commission it with a flue gas analyser and range rate it down for your heat requirements? I somehow doubt it with his attitude you speak of

 

[Agile]

Did he notify the installation to CORGI and have they sent you a Certificate?

This is an expensive and quite good boiler and its a pity if it was fitted badly by a cowboy.

Also to get the maximum warranty period it has to have been properly fitted by CORGI.

Tony

 

[ChrisR]

The poor old OP is possibly not much the wiser yet!

The behaviour is a result of air being trapped somewhere in tap water pipework. If the other end of a redundant piece of pipe is closed, (that is referred to as a "dead leg") then air can be trapped in it. It gets pressurised up to mains pressure. When a tap is opened anywhere, the air expands and the water in the pipes bounces around then, and when the tap's closed again. The boiler's water flow sensor sees some of this and starts to boiler working.
Though the disturbance stops quickly, the boiler has automatic "overrun" functions which extend its activity, such as the pump operation.

SOmetimes it can be simply a tap at a disused basin. Once the air's let out, everything's silent!

 

[Agile]

Well I am certainly wiser now!

I always thought a "dead leg" was when mine were crossed for too long and one went all "dead" and numb.

 

[gollancz]

Thanks guys. I'll get him back.
He IS CORGI-registered and has done all the paperwork....just doesn't seem arsed about this issue.

Just one clarification....
one of you suggested the dead leg could be where we removed an immersion tank (which we did) and one of you suggested it would be in the cold water tap system (we also removed a sink & bath).

Is either more\less likely? Not sure if all the capped-off pipes are still accessible....

 

[corgiman]

would not a shock arrester sort this without having having to access the dead legs?

 

[Agile]

A non return valve on the DHW outlet would almost certainly fix it.

In reality the air in the dead leg will probably dissolve over time and so the problem may go away on its own.

Its not good practice to have dead legs on water supply systems and its against water Regs on mains supply pipes. Since the hot water is now supplied directly from the mains then its probably illegal.

There is always a possibility that the air has not been fuly bled out of the boiler's store. Gas4U could advise if this is an installation requirement which your installer may not have met.

Tony

 

[gas4you]

I would go for the old hot supply that has been capped where the hw cylinder was. Can you see a 22mm pipe sticking out of floor capped off? If so it could be this. Easiest way out is to remove cap and fit a air bleed cap.

 

[stumpynut]

Sometimes unavoidable if the client does'nt want flooring/boxing disturbed, just get the installer to crack the cap end (if compression) not the best solution but sometims the only way

 

[ChrisR]

Is either more\less likely? Not sure if all the capped-off pipes are still accessible....

Could be anywhere.
Undo any "ends" you can to let any air out. Then leave it a week and see if it gets better.