No Hot Water When UFH Controller is On?

[BenH]

Hi,

My CH system is made up of 3 or 4 radio controllers. Each controller is responsible for a manifold & pump with attached number of UFH zones and radio operated room thermostats. I just found out that the flow pipe into the hot water tank (megaflo) starts to cool down rapidly when one of the controllers begins do circulate and demanding heat. When this is happening if I then turn off the mains to this controller the flow pipe (inlet) to the megaflow immediately gets hot again.

Seems like this problem was waiting to happen and just appeared after we had the first few cold nights.

In my mind this is some 'control' related issue. Is there a process by which I can shut everything down and bring it back up again so that controller(s) may operate without affecting the hot water?? BTW the UFH system is Uponor, if that matters.

Sounds familiar? Any ideas?

Thanks!

 

[Aquarius]

Sounds a bit like a balancing issue to me, where’s the hot water is being starved because of the heating being on. Either that or a failing zone valve.

 

[BenH]

Thanks, initially I thought along the same lines but the zone valve before the megaflo was recently replaced.

I had an inkling it had to be a controller issue but I don’t yet understand how physically it is possible. Even when I took the head of the zone valve off and manually opened and closed the valve nothing happened! It could be that the valve itself has gone faulty but then why as soon as I switched the controller off the megaflow inlet got hot again…?

So, first I had to figure out that the system (4 controllers in total) is configured so that 2 controllers (upstairs) are connected to an single interface and the other 2 controllers (downstairs) are connected to another interface.

I decided to RESET all controllers and set a new ID for each controller (took the info from installation manual).

I think it did the trick as the system is now much more stable in general.

Hopefully this has fixed it. looking good so far.

 

[Ben-gee]

Who replaced the 2 port valve before the megaflo?

On an unvented this should be a normally closed valve, ie power open, fail to closed.(eg Honeywell 4043H)

Possibly someone has fitted a fail to open valve ( E.g. Honeywell 4043B)?

I had a ‘B’ in an ‘H’ box once - of course I didn’t notice at time , couldn’t work out why the hot water was always on when heating was on - don’t know why they don’t just use an entirely different part number to avoid confusion....

 

[BenH]

Well, the port itself was not replaced, only the motorised head for the valve (U4043H) which was buzzing after 7 or 8 years. It is definitely the correct part. I was thinking one possibility is that there may be an additional valve (internal in the megaflo) which is linked to the controls? Could that be the case? Anyway, after controllers reset (as above) the system behaves normally.

 

[BenH]

UPDATE:
I've now traced the source of this problem (no hot water) to the Honeywell 7 day Timer (ST9100C). After 8 years of service it started to fail intermittently. This becomes clear when there is no click sound when changing between the 'off' and the 'cont'. There some help videos online on how to fix this ("capacitor issue") but as in my case the display began to blink as well so I just got a new one (Wickes). Finally hot water instead of lukewarm.