Cold water firing up boiler - Vaillant ecotec 837

[diywot]

Good evening chaps, I'm hoping some of you might be able to help. Excuse the long post but it might help to explain things clearly.


In previous winters, we've had problems with the pressure dropping out each time the heating was turned off. The FAQs pointed to repressurising the PV, which I duly did and seemed to do the trick: no more pressure drop outs.

This winter, the issue started again so I assumed I would have to repeat the repressuring. But before I managed to do that, we had a new radiator fitted in an extension room. Since THEN we've had a number of interesting developments:

- the pressure isn't dropping out anymore! (I know the plumber didn't repressure the PV)

- the radiators downstairs (nearest to the boiler) are heating well. A couple of ones upstairs are too. But on one side of the house, they're completely COLD! (They've all been bled) FAQs point to balancing the system, so I might have to have a go at that.

- every time a cold water tap is turned on, the BOILER FIRES UP. This is the most mysterious of the developments. I know for certain it didn't do this before the new radiator was put in. The display shows the hot water supply, the internal pump, the gas valve and the burner all in operation for a few seconds after it is turned on. This doesn't seem right at all..


I'd be very grateful to anyone who can shed light on the above matters, particularly the last one. A large quantity of kudos to anyone who might be able to assist. Cheers in advance!!

 

[planemad]

You have a dead leg of pipework somewhere which is causing this within your water supply pipe work is the normal cause of this.

 

[diywot]

Thanks for the response!

I looked into this, and that sounds like it could be the case. The only section of pipework that I can think of that might have ended up 'dead' is a hot water pipe which was capped off and made to disappear into a wall.

Can you tell me what the solutions are to a dead leg if I can't access it?

 

[St0rmer66]

Non return valve on cold inlet to boiler.

 

[ScottishGasMan]

A Dead leg in the Hot water pipework will only cause the boiler to fire for hot water when you turn the Cold tap off after running cold, it wont cause the boiler to fire while your running the cold.

If its firing for HW just after you turn cold tap off/or after flushing toilet, then dead leg for sure, which as said above Non Return/Check valve on cold inlet just under the boiler will stop it doing this.



If the boiler is firing as you run the cold tap and continues to do so with the cold water running then you have a pipework/mixing issue. which would need rectified properly. Not very common to get this tho, dead legs are very common.

 

[diywot]

Thanks for the replies guys.

Yup, it definitely seems to occur just after cold water is turned off. I imagine I would need a plumber to fit a non-return valve?

Are the other issues related to this, or are they separate? E.g. the pressure no longer dropping out seems odd.

 

[ScottishGasMan]

Depends on your DIY confidence. A non return valve will be a case of turning of the mains water in the house, cutting the cold inlet under the boiler and the valve its self is just a straight valve so slide it in (pointing the correct way lol) and tighten up

No the dead leg will have nothing to do with the Central heating system pressure, they are seperate water systems. Possible theres been a small leak where the plumber has Teed into the system which is now sorted as any water loss or venting of the system will drop the pressue.

If your gonna get someone to fit the non return valve, make it a heating guy who can take a look at the boiler + EV aswell. Opening the case to get to the EV is disturbing the sealed chamber of the boiler and as such is not subject to a DIY effort anyway.

 

[diywot]

Great, thanks for that comprehensive advice!

 

[gazdaz36]

One thing you could try is going into the d codes on the boiler. If you press the i and + button together. Then use the + button to go up to d88 and if you alter this it will cause a slight delay to the hot water start up.