No Hot Water to tap Unless I turn on the Cold tap too!

[nme]

Helloo all.

I have a Worcester Bosch 30CDI conventional condensing boiler (still under warrantee) together with a Heatrae Sadia 250Litre Megaflow in the loft. I Also have wet underfloor heating which is run by the same boiler.

This was all installed within the last year, and as I mentioned, is still under warrantee etc. One friday I had the electric board around to change my elec meter for a new one - apparently standard procedure after some time period. When they did this, they had to turn off the power to the whole house for about an hour. Now I don't know if this is related, but the next day, I was not able to get any hot water from any of the taps in the house. I Checked the boiler and it fires up fine when i turn on the hot water on its own, or perhaps just the heating too. I can feel the pipe running out of the top of the boiler and up to the loft is boiling hot. The pump on that pipe seems to be running as well. So I Know that water is being heated.

But when i go to any tap in the house, and turn on the hot water, all I get is cold water! After some playing around, I noticed that if i turn on the hot tap at the basin, then turn on the cold tap elsewhere ( bath, kitchen sink, shower etc ) then the hot water in the basin runs hot!

How odd is that? Can anyone help?
I've rung up the boiler manufacture and they can send someone in a couple of days, but i'm not sure if this is a boiler problem, or should I ring up the plumbing company who installed it? Or is there something simple I have missed altogether?

I thought it may be an airlock at first, but looking around on the web, the symptoms are not the same.

What could this problem be?

Oh, also, I've checked the electric breaker, and everything is switched on.
thanks
nme

 

[gas4you]

Strange. As your hot water is supplied from the megaflo which is indirectly heated by the boiler then I do not think it is anything to do with the boiler.

As the hot water comes out hot when a cold tap is used then that is evidence that the boiler appears to be coming on at some point to heat the water.

If the cold taps you are turning on are on the balanced side of the prv at the megaflo then this could influnce the delivery of hot water if the strainer has become blocked or the prv is not functioning properly.

If the cold tap is before the prv then I cannot see how this will affect the hot taps. Is this basin tap a mixer tap?

Check the strainer on the prv is not blocked first of all, then I would drain some water out of the megaflo and refill it with a hot tap open.

It is very rare to get airlock problems with unvented cylinders.

 

[nme]

Hi Gas,

thanks for the reply - not sure what a prv is - primary return valve? (what's one of those?)

All the taps in the house are mixer taps, and the same scenario applies to any of these. On one tap I have to turn on the hot, and at another, the cold to get hot water out of the first tap.

Happy to check the prv / strainer - if only I knew what to look for? What exactly am I looking for?

With regards refilling the megaflow, am I to assume, turn of the cold water mains, and run all the hot taps until the megaflow is empty? - then turn on the mains with all hot taps open?

 

[gas4you]

Pressure reducing valve (or balancing valve) With the megaflo this is the big black contraption that holds the on/off 90D tap, probably near the megaflo at the top in the pipe work.

I am clutching at straws with this though.

If the water wasn't getting hot then I would suspect the dhw/megaflo cut off zone valve. Apart from this I can't see what effect the power going off would have had.

Others on here may have other advice to give

 

[nme]

Thanks Dave,

Will take a look tonight in the loft. On the whole though - I'm guessing this looks to be a problem with the plumbing rather than the boiler - correct? If its the plumbing, I should be calling out the plumber, not the boiler manufacturer's chap.

THanks for all your help

 

[gas4you]

I would agree that its probably nothing to do with boiler. Bear in mind that you will need a plumber with the unvented G3 ticket. I take it you will call in the one who installed it?

 

[nme]

Hi Dave,

yep, i will be calling in the guy who initially installed the system. - What's the G3 ticket you mention? Not heard of that before? How do I check if the guys that did this originally have that ticket? or if not, how do I find one that does have that ticket? Any reccomendations for the North West London area?

Many thanks for your help

 

[penpusher]

think agile is in your area.

 

[corgigazza]

I would say that you have a faulty mixer valve on the shower or tap, also possible bleding valve fault.

to test this turn of mains water to hot water cylinder then drain of pressure, if it will not stop coming out of hot tap this indictes that fault you can some times hear the shower noise at the valve of hot water getting by, also the valve will be very cold.

 

[Dan Robinson]

I thnk several of us are in NW London - you'll be waiting a good few weeks for me though...

Ask to see the guys G3 qualification card - I carry mine, as I am sure Tony et al do.

If he doesn't have one then you should have had the local authority sign it off.

Don't let them fob you off with BS, it is the law - just like CORGI is for gas engineers.

 

[nme]

I would say that you have a faulty mixer valve on the shower or tap, also possible bleding valve fault.

to test this turn of mains water to hot water cylinder then drain of pressure, if it will not stop coming out of hot tap this indictes that fault you can some times hear the shower noise at the valve of hot water getting by, also the valve will be very cold.

Hi Gazza,

All the taps and showers are mixers in the house, and this problem is right now effecting every tap. If this is a problem with a single mixer valve - that would only affect that tap - not the rest in the house - or would it?

About testing this - I can give it a go now - If i turn off the water at the main stopcock under the sink, then run the hot water til it empties the megaflow, or do you mean to drain pressure not water? - if so, how do I do that? I'm going to a have a little tinker tonight, but likely leave this to the pro's.

Thanks for all the help so far chaps - I'm going to get the original plumber in, and see how that pans out!

 

[nme]

I thnk several of us are in NW London - you'll be waiting a good few weeks for me though...

Ask to see the guys G3 qualification card - I carry mine, as I am sure Tony et al do.

If he doesn't have one then you should have had the local authority sign it off.

Don't let them fob you off with BS, it is the law - just like CORGI is for gas engineers.

Thanks Dan, I'm sure they are ok - I believe they are a legit operation, but never heard of G3 before - will be checking though

thank you.

 

[nme]

Hi All,

just thought I would follow up on this to close the thread.

Had my original installers in today, and after they finished laughing, when I told them that to get hot water I had to run the cold tap, they spent about thirty minutes running between the loft and the bathroom.

The upshot is that the problem is now fixed (fingers crossed) and the problem was as mentioned earlier by Dave, a result of the PRV filter being all gunked up. They mentioned that a lot of the gunk in the filter was the stuff they used to 'weld'? the pipework when they installed it, so dont expect this problem to reoccur again any time soon, and was likely because this was a new install.

The great thing is that I now have hot water again to all taps.
I could not really understand why I was getting cold only on a mixer tap when i had turned on just the hot tap, but they believe the problem could be related to one of the taps in the house which has a single tap which mixes the hot and cold depending on which way you turn it.
They explained that normally, with my other mixer taps, i have two taps - hot and cold, whereas on this one tap i have just one, so turning it on will allow both the hot and cold feeds to open, and this is where they thing there was some 'crossflow'? Not sure what that means. But in short they tell me that they think this is now fixed, and shouldnt expect it happen again any time soon.

What do you guys make of that? Should this filter really get blocked so quickly? The install was about eight / nine months ago.

And what do you make of the theory of why i would only get a cold feed when i turn on a hot tap?

Either way, I'm a happy chappy, and thought these guys were top.

Also, many thanks to all on here who responded

thank you!

 

[gas4you]

Glad its sorted! It can be a problem after a new install to get debris in the pipes, that is why a ch system is flushed during commissioning.

I think it has just been bad luck that the solder, I presume, had been applied a little too generously and a bit had blocked the prv strainer.

But then I think tjis problem is better than an installer who uses too little and risks the joint 'blowing apart' under pressure.

Glad we could help.

Not too sure about the tap thats left though, unless it is as described in a previous reply or faulty!

 

[kjharry]

If the problem was cross flow of cold water into the hot pipes via a non-biflow mixer tap by having the mix lever in the middle,that is hot+cold running together,then check valves (non-return valves) on the supplies to that tap would stop it happenning again,flux in the strainer is another problem though,from not flushing pipework on commissionning the system,the lack of cold water flow into the cylinder through the strainer and obviously the resulting lack of hot water out the other side would have made the tap problem more pronounced bygiving you unbalanced pressure to that tap (and to all the others).