Help protect 3-port valve by switching off hot water last

[Jimk]

[MM]

My heating engineer, who is very good and always does a good job, fitted a new 3-port valve in the airing cupboard last week. He replaced the Danfoss with a Honeywell. The Danfoss has lasted 15 years. He explained how these valves work and said that it was always better, if possible, to have the hot water switch off AFTER the heating, because this guarantees less wear on the valve due to the way the valve positions itself when the hot water is switched off. Even if one has the central heating on and it is then turned off, it's a good idea to switch on the hot water briefly, even for only 30 seconds, so as to reposition the valve beneficially.

MM

[Harry Bloomfield, Esq.]

MM used his keyboard to write :

I don't get it, or the logic?

Unless there is a call for CH, then a spring return 3-port valve will always return back to the HW position, which is the reason they suffer so much wear - constant back and fourth motion. They need to be powered by the call for CH, to be moved away from the default HW position.

A momo 3-port valve actuator is much better is this respect, they default to staying put to match the last call for CH or HW. momo = motor on/ motor off, no springs involved, hence much less wear, much less movement of the valve.

[The Natural Philosopher]

In the same way that te correct place to leave a toilet seat is where ypu put it to use it.

That way there is a 50% chance of it being in the right place for the next person.

[John Rumm]

That's because with all demands satisfied, the grey control wire to the valve is left live. However that is only connected to the motor via one of the microswitches which are activated either side of the mid position of the valve. Hence if the valve was in the heating or heating + hot water state, when the system enters the "all done" state, then it will remain connected to power - and be driven to the heating only state where it will sit, with the motor under power but stalled until the next demand for heat.

If the last state of operation was DHW only, then the valve will be in its unenergised state with the spring pulling it back to the DHW only position. Since neither microswitch will be activated in this position, the live grey wire will not be connected to the motor, and it will now rest in the unpowered state.

There is a control circuit mod that you can do to "fix" this:

[MM]

Very interesting, thanks!

MM

[Michael Chare]

I would have thought that 15 years was quite a good life span. The motors of my momo valves did not last that long.

[Tim Lamb]

I beg to differ. If the next user is male, he may require the seat up or down depending on need:-)

>

[Tim Lamb]

In message [e-mail]>, Tim Lamb [e-mail]> writes

Someone who knows more about statistics than I may chip in but, after writing the above, I wondered if the sex of the next user did really make anything different.

[Harry Bloomfield, Esq.]

Michael Chare explained on 12/12/2019 :

Exceptional longevity! Mine tended to last 18 months to three years.

[tabbypurr]

That ain't right. The 3 position valve's positions are, in this order: HW only (resting position), both on, CH but no HW. So the way to minimise wear is to not turn the HW off at all, jus leave it move between HW and both.

NT

[MM]

My heating engineer was gobsmacked that it had lasted that long, especially for a Danfoss brand, which he doesn't rate very highly.

MM

[MM]

My neighbour, whose house is identical, has had three replaced in the

15 years. Must be the way I've used the heating that's kept mine working all this time.

MM

[MM]

But then I'm going to have far more hot water than I know what to do with. One hour with the Wallstar gives me enough water for a hot bath AND the washing-up.

MM

[tabbypurr]

Once it's hot it stops heating it.

[ARW]

Ready for the annual bath then?

Best take the washing up into the bath with you to save some money.

[Graham.]

My pair of Honeywell V4043 2 port valves lasted at least 42 years, from the time I bought this house in 1977 until March this year when I got a new system. They were the old type that didn't have a removable head. It was a little bit "Triggers Broom", in that the motors and microswitches had all been replaced by me two, if not three times, but the "wet" side of the valves were original and never gave any trouble. I put it down to the soft water.

[John Rumm]

One common cause of failure is that of the motor - and that can be a separate issue from wear on the mechanics.

If you look at the "normal" Y-Plan circuit:

Imagine the the programmer has DHW "off" (i.e. the "HW off" output is live and the "HW on" one is not), and it and the stat are both calling for heat on the CH. The valve will move to position A or "CH only", and both microswitches will be closed (they are both open in the port B or spring return default position). The room stat now, reaches set point and opens. So there is no call for heat from either CH or DHW. However because SW1 is in the position where the grey wire is connected to the motor, and the wire is live because "HW off" is live, the motor will remain powered, and the valve will stay in position A.

Should the programmer demand DHW now (even if the cylinder stat is still satisfied), "HW Off" will go low, and power will be removed from the motor - and that will allow it to spring return to the B position.

[MM]

Sure -- but only for a while, as the temperature will inevitably fall and the boiler will kick in again. If I've had my bath that day, how can I justify having a copper cylinder full of very hot water until the next day? Seems daft to have piping hot water at 3:00 a.m. at night.

MM

[MM]

Is this comment supposed to be funny, Mr Troll?

MM