I have a Potterton Profile 40el-80el boiler, a Drayton 2 port mid position valve (BGMUSP-23) fitted and a RS1 Room stat.
The problem is the boiler fires up intermittently when the room and boiler itself get cold. It will not ignite when you manually turn up the room stat in between these times. After a couple of hours, it will ignite again and run for approx 10 mins then turn off again?
I was wondering if anybody has experienced a similiar fault or could offer any advice on what to check? Ie is it a faulty room stat (do they go faulty) or a fault on the valve of a thermostat problem with the boiler itself. Your advise would be aoppreciated.

Terry, March 2010

I have the same problem, I think its the motorised valve not working, I can have the heating on and get relative luke warm water, but if the heating is off I will have only cold water, the pump works when asking for heating but will not fire up when asking for hot water only, I am considering changing the motorised valve any assistance would be welcome, is the wiring very hard to change from one unit to the other, ?

Paul the amateur, April 2010

Peccavi / John & hi-spec plumbing & heating (essex)

As a thank you I'd cut all your lawns, but me to, I'd pass on the baby thing.
I managed to get a replacement valve, Drayton MA1, (3 way not 2 way as I previously stated in error). I turned of the power to the wiring unit and changed the valve over wire for wire. Then the nervous part of switching the power back on, it worked.

When the room stat was turned up i watched the lever move to the C position and the boiler fired up.....it wasn't doing that before.

Thanks again chaps for your help and I agree this forum is certainly very useful.

Terry, March 2010

peccavi, i hedged my bets and decided it was the motorised valve, do i get my lawn cut for that if right? i will pass on the babies, we have 4 aged 15 years to 6 months, i enjoy reading your well informed answers and think you help to make this a really worthwile info and idea share website,

john, March 2010

won't be a pump issue the pumps running on hot water.
switch the programmer on heating only.
turn stat up to about 25 c.
is the stat getting a live ?
is the white wire of the mot valve getting a live ?

check all them before waisting money on parts.
why buy a complete valve if not needed.
>Drayton BGMUSP-23 2 port valve - is not a 2 port it's 3 port mid position valve.

hi-spec plumbing & heating (essex), March 2010

Me and John are slightly in dispute over this - he has the experience but...

The Pump is a Passive Device - it has no control over the boiler whatsoever. The pump is told to run when the boiler is fired up and it runs until the boiler stops firing with a little over-run to clear the heated water from the heat exchanger.

All the pump can do is move water through the heat exchanger - if it does it poorly or not at all then the overheat safety stat will switch everything off - this is not happening - therefore, the pump is eliminated as a possible cause of the - failure to fire-up problem.

I have never actually looked inside the head of a MPV but I know it has microswitches and I know that little switches can fail, get moved slightly, are relatively easy to replace, don't cost much (if you can find one) and are easy to test if you have a meter.

In the interests of saving you money suspect the switch first - it's a 50p item.

John, if it turns out to be the pump I offer to mow your lawn for a year and have your babies.

I know nothing about boilers and still have no experience.

Continuing good luck...

Peccavi, March 2010

Many Thanks again for your advice

I think I'll try and get a new valve fitted today or asap. Is the Drayton BGMUSP-23 2 port valve readily available at most plumbers merchants?

I'll let you know if this works...Thanks again.

Terry, March 2010

ps try opening the motorised valve on the heating circuit manually if it isnt opening via the stat, pushing the lever to make it open will heat your system if you lock the lever off or hold it open this will prove valve failure if it makes the heating work i should have mentioned this before asking you to check the pump, if this works it is the valve i would change the whole thing and not mess about with microswitches , motors etc

john, March 2010

keep it simple there is a lot of advice below from people with knowledge but i would be bogged down with all that, if your boiler fires up even for short periods i would be satisfied the fault is in the system, the only way really to know its the pump is to change it, you could have air in the system but my strong hunch based on quite a lot of experience is your pump has failed, if the valves each side turn off it can be straight forward but often the union nuts are tight and the pump vavlves let by and it can be a nightmare, good luck and i hope im right

john, March 2010

A faulty pump may cause the boiler to stop working but the overheat stat will trip and it's not tripping - you can assume then that your pump is fine.

For - central heating only - the control signal comes from the timer/programmer then to the room stat and then to the Mid Position Valve - the valve motors fully over to the C/H position and in doing so makes microswitch 2 which then sends a turn-on signal into the boiler on the Orange wire.

Your boiler system is not doing this - I still suspect the control head of your MPV and particularly the microswitch - but I am still guessing - might it be the motor? I don't know - one or the other.

Continuing good luck...

Peccavi, March 2010

Thank you gents for your answers. I can add a few things from the questions you asked, it may narrow things down a bit!
a) The boiler will not ignite by turning up the room stat at any time, however the boiler will ignite when the Hot Water cylinder stat is turned up, ie requesting Hot Water.
b) Yes there is an overheat stat, situated through a little hole at the bottom of the boiler. This has not tripped so far.
c) Yes this is a new fault, the system has been working perfectly until a couple of days ago. Is there way of testing the pump, to see if it's faulty?

Do you think these symptoms could be caused by a faulty motor situated within the Motorised valve?

Thanks again for your help

Terry

Terry, March 2010

has this system got a frost stat fitted ?
that number is a BG number and its a 3 port not 2.

> It will not ignite when you manually turn up the room stat in between these times.

what times ?

>My guess is an issue with the Mid Position Valve - specifically the microswitch with the Orange Wire - SW2.

for power to the orange you would need power to the white from the room stat.

hi-spec plumbing & heating (essex), March 2010

faulty air pressure switch in the boiler may cause this fault.
you are much more likely to notice the fault on the heating than the water unless you have used a lot of hot water.
doubt very much that the room stat is faulty, possibly a fault with the actuator but it's difficult to tell without setting about the wiring centre with a multimeter.
it may be a slow running pump, though i would expect a fair bit of noise and the overheat stat would probably pop.
one other thing to check is if the pilot is still lit with no demand on the boiler, this indicates a faulty gas valve and will cause the same fault.

Ian, March 2010

I am an unqualified muppet when it comes to boilers - my opinion is worthless...

If the pump failed or were failing then the overheat stat would trip and need to be reset - I assume this boiler has an overheat stat?

My guess is an issue with the Mid Position Valve - specifically the microswitch with the Orange Wire - SW2.

In the C/H only condition the signal to fire the boiler comes from this switch - and the boiler appears not to be firing for C/H only.

The firing for 10 minutes now and again may well be a request for the boiler to warm up the hot water cylinder. In this condition the C/H will also be called so the heated water will be shared and the rads will get warm. When the cylinder stat is satisfied it's back to C/H only and the need for SW2 to send the fire-up signal.

But I'm just guessing and have no boiler experience...

Good luck...

Peccavi, March 2010

is this a new fault or has the system allways been this way? if its recently developed it sounds like your pump is failing so the boiler thinks it is up to temperature, stats dont usually fail, digital or remote ones are less reliable, zone valves usually fail open or closed, so start with the pump they can sound like they are running but if the impellar has snapped from the shaft it wont pump much

john, March 2010