CH & DHW switching issue

[condeh]

Hi,

I have read through the FAQ, so apologies if this is a rehash, but I can't spot my problem in there.

Basically, I cannot get CH and DHW to work at the same time.
The equipment is as follows

Boiler : Ultracom 15hxi
Remote Thermostat/Receiver :BRTRF/BR1
Timeswith/Programmer : iflo (24hr mode)

We have been here 1yr, and no problems. Away for a few days and came home to cold house. Turned up thermostat as usual, shows call for heat sign, but boiler doesn't flash up.
Went up to check timer HW is on 'TIMER' and CH is on 'ON'.

Much faffing later I have the following.

If both DHW&CH are showing as powered up on the timer, and I initiate a call for heat from the remote thermostat, the mid-position valve will stay in the 'W' position, and the boiler will not flash up, until I switch the DHW 'OFF' on the timeswitch/programmer. Once put to off, the MPV moves across the 'H', boiler lights, no problem.
Now with CH 'ON' and DHW 'OFF', if I turn DHW back on, and turn up cylinder thermostat to initiate a call for heat, nothing will happen until I turn CH to 'OFF', then the MPV moves to 'W' and boiler heats the water.


Irritatingly, last night the MPV did move to the centre 'M' position a couple of times when both CH and DHW called for heat, this was after I had played with the timer a bit and I thought I had cracked it. Went to bed but this AM now cannot get them to work together as described above.

In summary. I can get CH *or* DHW, the room thermostat and the cylinder thermostat both appear to be initiating a call for heat and receiving heat, but only when the other is turned off (even momentarily) on the timeswitch. I need to switch one off for the other to work, even if neither are calling for heat at the time.

My uneducated guess is that the MPV is having some sort of trouble, as all the communication routes appear to be working, except at the MPV. The fact it did work last night tho is confusing.

Many thanks for any advice.

 

[Blagard]

Sounds like the microswitch in the three port valve is faulty. SW2 on the illustration in the link. Power to the motor need to come via SW2, half rectified through the diode and reduced by R1 to stall the motor at mid position.

See
http://www.gasheating.co.uk/Mid-Position-Valve.html

The easy solution would be to replace the head complete.

 

[condeh]

OK, thanks for your help.

So a faulty SW2 would not only result in a failure to find the mid position, but also cause the MPV to essentially be stuck at one end or the other until the DHW or CH is manually turned off and on?

My understanding would be that if I put the valve to the manual position in the meantime, that both the DHW and CH will work 'on demand' but when one is running, so is the other?

Thanks for your time.

 

[stardanny]

Yes, MPV is faulty. Replace valve head.

Yes, manual position will keep both port open but has no thermostat control on other while one is in demand.

Dan.

 

[Blagard]

OK, thanks for your help.

So a faulty SW2 would not only result in a failure to find the mid position, but also cause the MPV to essentially be stuck at one end or the other until the DHW or CH is manually turned off and on?

My understanding would be that if I put the valve to the manual position in the meantime, that both the DHW and CH will work 'on demand' but when one is running, so is the other?

Thanks for your time.

Yes your valve motor is getting no power (hot water position) or full power (CH position).

As the valve motors are a more common failure I would suggest you hang onto the old one as a spare for the future (take it out of the old head when you replace it)

The manual position is really for venting the system only and you are correct that CH and HW are both running when you do that.

The valve heads are usually fairly easy to replace but shop around as prices vary enormously you don't need the complete valve, just the head so no plumbing is involved

 

[mogget]

Also if set to the manual position it will usually click back to auto after central heating has been called for.

 

[condeh]

OK, so I have replaced the MPV with the same model again, and still the same problem. The valve will sit at either W or H, but never M.

To get HW to work, I need to cycle through the CH from on to off on the programmer. Opposite is req'd for CH to work.

I'm stumped. I'm sure I have wired the replacement the same as the original, and the original worked for the year we have lived here.

 

[Blagard]

Time to check the wiring! In particular the live feeds to the MPV.

Disconnect the orange , grey and white MPV wires and check the terminals they normally connect to.

Switch CH and HW on

Orange terminal should be Live (this is the HW on)
White terminal should be Live (This is the CH on)
Grey terminal should be Off

This is to check that the supplies that normally activate the MPV are correct before the MPV moves and engages micro switches

 

[condeh]

Thank you for your quick reply, I have a multimeter in the post now, so tomorrow will get back to you with results.

Many Thanks.

 

[Blagard]

Just so you are aware.

When the Hot water cylinder reaches it's set temperature the cylinder stat will turn off the HW and so the valve cannot go to the mid position. Then the Grey wire will be live

Hopefully you were testing when the cylinder was still cold enough to actually call for heat!

 

[condeh]

At each time I am turning the cylinder stat right up to stimulate a call for heat. Having done that the valves does move to W once I have turned off the CH.

 

[Blagard]

At each time I am turning the cylinder stat right up to stimulate a call for heat. Having done that the valves does move to W once I have turned off the CH.

See edit above if Grey terminal is live that means HW is Off

 

[jeff the gasman]

If you have a wireless RF room stat I would be looking at that first. They regularly lose their connection an give us guys headaches and bad names.

 

[condeh]

OK

CH & HW set to "ON" on the programmer.
CH & HW termostats turned up to max.

White, Grey & Orange wires disconnected.

White = Off
Orange = Live 240
Grey = Off

 

[Blagard]

You need to trace back that white terminal as with CH on it should be live.
The white wire terminal should be the switched live from the Room Thermostat.

I suspect the present white wire terminal is not the switched room stat. it may even be to the HW off terminal from the programmer.

Untitled

• Blagard
• 18 Mar 2014
• 1