CH DHW wiring / plumbing problem

[Illuma]

Hi, It would be really helpful if someone here can help shed some light on this problem please. The situation is my mother in-law has just moved house and the CH/DHW system is wrong, I am hoping to get it back to some type of functioning system for her. Here is what happens...

The programmer is set to fully pumped it is a RWB9.
The DHW is an indirect cyl in the loft, it has 15mm pipes to the heating coil!
There are NO room / cyl stats in the system.
I know the valve (two way VAL222MV spring closed) has a duff motor and previous owners have set it to manual.
Please see attached picture for plumbing / wiring diagram. I have omitted returns and neutrals etc for clarity.

I know when you look at the wiring diagram you will say that its wrong I know that because you can workout what happens when the programmer is set to CH only!

I just need some help on what the best way to sort this mess out is? I don't really want to do any major changes to the system. I don't really think the system follows any type of plan, the nearest I got to was an old W plan with priority to DHW but with no stats??? Is my best way to fit room / cyl stat, new two way valve and give priority to DHW?

I hope giving the priority to the DHW will heat the water in the cyl, at the moment you obviously have to have the HW on to get the CH to work due to the wiring, you can leave the CH off as the valve is set to manual as it duff! Setting the system to CH only does nothing because the valve motor is duff and the wiring is wrong. So what we have at the moment is when the DHW and CH are on the rads get hot but the DHW stays cold, if you feel the pipes in the loft they hardly get hot, this I put down to the 15mm they are plumbed in! I am hoping fixing the valve and giving priority to the DHW will give enough pressure to actually get the heat to the cyl? If I get chance tomorrow I will test this theory by closing the valve and seeing if the heat gets to the cyl.

Thanks in advance.

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[ChrisR]

Cheapest would be to add a room stat and a cyl stat and convert to C plan.

Better would be to add a 2 port valve and convert to S plan, though that may need a bypass depending on the boiler.

15mm to the cylinder is common and usually works OK. If it's in the loft though the primaries for the cylinder filling with air will stop it.

 

[Illuma]

OK, converting to S plan would be simple enough, the boiler is a Baxi WM 51/3RS. Would I need a bypass? If so what do I need for that?

Thanks

 

[twgas]

as it is the prog doesn't need to be on fully pumped as you can't have heating without HW.
I would suspect an air-lock in the flow to cyl is the reason for not getting HW.

 

[Illuma]

as it is the prog doesn't need to be on fully pumped as you can't have heating without HW.
I would suspect an air-lock in the flow to cyl is the reason for not getting HW.

I agree, I was just looking at the S plan and when there is a demand for DHW and CH both valves open, neither has priority. This leaves me in the same situation we have now I can have the pump & boiler on, the valve for the CH is open so CH is on and as it stands there is no valve on the DHW so it is also on. This still leaves me with the problem the at the moment the DHW wont heat up. As you say a good chance of an air lock. When I have looked in the loft the pipe that would come off the top of the heating coil in the cyl has been recently modified to tee into the pipe that comes from the CH water tank, I assume original design was the pipe looped over the top of the CH tank in case of air locks / boiling? Any idea why it was changed to this way?

Is the best method of removing the air lock to crack open a compression fitting?

I must question is there something like the S plan where you give DHW priority over CH, but when the DHW is at temp then the valve closes and all the heat is only passed through the CH circuit?

Thanks in advance

 

[twgas]

The tee from the coil to the, I presume, cold feed doesn't sound correct. It was possibly done to get rid of the air, a pic of the pipework in the loft may help, if that's possible.
Cracking a compression fitting is a method of releasing air, I wouldn't say the best though.
I don't know of a HW priority S plan, cant really see the point, but it may be just a question of playing with the wiring.

 

[Illuma]

The tee from the coil to the, I presume, cold feed doesn't sound correct. It was possibly done to get rid of the air, a pic of the pipework in the loft may help, if that's possible.
Cracking a compression fitting is a method of releasing air, I wouldn't say the best though.
I don't know of a HW priority S plan, cant really see the point, but it may be just a question of playing with the wiring.

Hi Thanks for the reply.

OK, here is where we stand today! I have got the DHW pipes hot, I think there was an air lock and the pump was set to 3, I changed it to 2 and things started to get hot. The Tower valve fitted when closed still heated the CH so I will rip it out and replace with better quality at the same time as converting to S plan so hopefully all the problems will be sorted.

Thanks for all the help.

Best regards & happy new year.
Mark

 

[Illuma]

Ok, Sorry for the delay I just have not had time to get any photos. I have added another sketch to show how the vent has been modified.

The feed and return to the CYL coil is in 15mm as is the feed / vent from the header tank, the yellow dashed part is what I assume it was like before with out the bit in red as there is a cut out in the header tank lid and the bit in red is what it is like now, the bit in yellow has been removed, all the pipe work on this area is 15mm.

I don't think this is right, but then I am not a plumber by trade! Things have changed allot since I did a bit of plumbing.

My mother in-law has also asked a plumber that has done work for her before and he says converting to S plan is very expensive and pointless as some of the rads have TRV's and she will gain nothing by changing how it is now? He also quoted at least £150 to change the zone valve, I have a brand new spare Honywell one but he wont fit it unless he supplies it? I think he is talking c**p.

Any help on the vent is appreciated and feel free to correct me if the plumber is right in what he says.

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[twgas]

I would suggest converting to a properly controlled S plan system would be fairly simple. Change the CH valve if it's dead, Add HW valve where the 22*15 reducer is and a few wires.
The awkward bit might be the pipework, you'd need vent and feed (or a combined feed/vent is boiler suitable) ran down to join system between boiler and pump.

 

[Illuma]

Hi Mick

Thanks for the reply, unfortunately the house was house doctored! Laminate flooring and all that, so major work is off the list at the moment. Can the filling be kept as it is now? Also can you confirm if the combined vent / feed is OK as it is? I assume they have had problems in the past with the amount of tweaks done to the system. Should the vent / feed not be in 22mm? Why would they modify the feed / vent, what problem could it cure?

Regards
Mark

 

[twgas]

What boiler do you have, you might be able to convert it to a sealed system, or moving the pump might be a possibility. Yes a combined feed and vent should be 22mm, the vent should be 22mm even if it is seperate to the feed.

 

[Illuma]

What boiler do you have, you might be able to convert it to a sealed system, or moving the pump might be a possibility. Yes a combined feed and vent should be 22mm, the vent should be 22mm even if it is seperate to the feed.

The boiler is a Baxi WM 51/3RS. Converting to a sealed system is a possibility but I am trying to take cost into account for her as well, what would it roughly add to seal the system, I assume I would need an expansion tank but what else?

Thanks
Mark

 

[twgas]

Your (her) boiler is not suitable, without an upgrade, for conversion to a sealed system, also a combined feed and vent would be inadvisable. I don't know if the sealed system kit is still available.
Is moving the pump a possibility, ie where is the tee supplying the CH valve and HW cylinder.

 

[Illuma]

Hi Mick

Thanks for the help! Moving the pump is possible, wiring may be harder but also possible! Currently the pump and the CH/ HW are easily accessible under the floor in the cloak room as is the zone valve etc, the house had an extension so the boiler was moved from the cloak room to the extension approx 5 feet, to keep the flue external and gain some space I guess.

Roughly what are you suggesting?

regards
Mark