Combi Boiler Comes On Briefly As Cold Water Is Run

[pbar]

Thanks very much for your concise and definite answer.
One futher question I have, if the non return valve was connected to the hot water out (thereby eliminating the need for a mini expansion vessel), would it still solve the original problem I have of the boiler coming on when cold water is run, or is it more effective to put the valve on the cold water in. Thanks for your patience!

 

[Gasguru]

1 Get yourself another plumber since he hasn't a clue.

2 Remove the cap on the washing machine pipe and fit a standard washing machine valve. Connect a standard washing machine hose and run off a sufficent amount of hot water to make sure there is no longer any trapped air OR cut back the pipe to where it tees off the hot feed.

If you put a non return valve on the cold inlet to the boiler this will probably solve the problem, however you should fit a mini expansion vessel downstream of the valve to prevent excessive water pressure build up. Unless the mini expansion vessel is maintained on a regular basis ie yearly (and they never are) you run the risk of high pressures building up and a subsequent water leak. Therfore getting the air out of the hot pipework should be the first course of action.


The mini expansion vessel is to accomodate the extra volume of water as it is heated when you close the hot tap (residual heat transfered from the primary water in the DHW calorifier). Normally this small volume of water is allowed to expand back down the pipework. If a non return valve is fitted the expanded volume can't do this and excessive pressures can build up causing damage.

Getting rid of the air is the priority since the non return valve /expansion vessel on the boiler cold inlet will not necessarrily solve the problem if you still have air in both the hot and cold pipework.

 

[pbar]

Cheers for your post and points. I will do as you say with the washing machine hot water.
Please forgive my ignorance, but when you say that the expansion vessel should run downstream, then it should be fitted after the check valve. i.e. the expansion vessel should be fitted in between the check valve and the boiler? Thanks.

 

[timbalcombe]

I had this trouble and it was the washing machine was stuck on some weird setting where i had to turn it on to use a setting which drew hot water eg a 90 degree wash. It worked for me.
I had managed to trap air after I turned the water off into the house and on again.

 

[pbar]

I've had a look at my not-currently-used hot water supply to the washing machine, and the actual outlet (which is now capped) is plumbed in line with the hot pipe which feeds the tap to the sink, so there isn't any unused pipework there, so I don't think that can be the issue in my case.
My plumber is fitting a non return valve and expansion vessel today, hopefully that will cure it and all will be hunky dory again.

 

[pbar]

Well, my plumber installed the check valve and expansion vessel, just hope he's done it right. It has solved the problem, thanks again for all who offered advice. Please have a glance at the pics, and shout if my not so brilliant plumber has messed something up. There seems to be an awful lot of ptfe tape around the expansion vessel joint.

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[pbar]

Please could someone have a butchers at the pics and tell me if it looks ok at first glance. Cheers.

 

[Gasguru]

Looks OK to me - easy access. The threaded connection may have been quite loose requiring plenty of PTFE to ensure a water tight seal.

Just be aware that the air pressure in the vessel will drop over a few years and the protection the device provides against high water pressure build up will be lost.

Re-charging the pressure vessel is quite difficult with a foot pump (as the air pressure is easily lost as the pump is removed from the valve) and a portable air compressor is a better bet.

When checking the air pressure the stopcock must be off and a hot tap open.


Since this was an illegal boiler move you may like to clarify the following with your builder/plumber/Corgi

The gas pipe may be undersized since we can only see 15mm pipe - perhaps it reduces from 22mm a little further up the wall.

Electric cables appear to be in close proximity to the gas pipe.

The filling loop does not comply with the water regulations.

There is a fair amount of "snot" on the pipework indicating poor soldering practice (lazy) ie the joints were not cleaned of flux residues.

Hope this isn't to techy for you

 

[pbar]

Thanks a lot, appreciate it.

Thanks for the advice about the expansion vessel.

Yes, you are quite correct about the gas pipe, it is 15mm, but it is reduced from 22mm. It was 22mm before when the boiler was in it's other location, they joined the 15mm to that and took it to the boiler. Is that ok.

The white cable you can see runs to the control panel on the wall. Is that illegal.

Please could you tell me the problem with the filling loop

Cheers.

 

[clf-gas]

Made very interesting reading this post and threads as interesting as the posts on certs/legallities pbar. Now Iam sure you understand why we will take boiler off wall, LIFT FLOORS TO CHECK PIPEWORK

OK now your last post:-

The white cable you can see runs to the control panel on the wall. Is that illegal.

Would be better if programmer was on the wall left of the boiler, cable would then be away from gas pipe.

Please could you tell me the problem with the filling loop

Disconnect one end and then nothing is wrong with it.

Cheers.

No No your welcome sir.

 

[pbar]

Thanks very much.

Concerning the gas supply pipe being 15mm. Should this really be 22mm.

Cheers.

 

[clf-gas]

To be honest, I would have brought the 22mm feed to the boiler rarther than reducing from what is out of frame in pictures. Going off what I can see I'll gestimate theres 3m equivalent length of 15mm, 3 Possibly 4 elbows is equivalent to 1.5 / 2m of pipe and a further 1 / 1.5m of 15mm.

Iwont say its OK and i cant say its wrong without checking pressure drop at appliance.

 

[Gasguru]

Without calculations even 22mm may be insufficient - this is why builders and non gas qualified installers should not move boilers.

The filling loop should have the double check valve on the cold side, however disconnecting and capping the fitting ends (with washers) will suffice although not strickly compliant.