...if anyone's able to answer.

I recently had some central heating work done - system converted to a sealed one plus an unvented hot water cylinder fitted. At the same time I had the boiler serviced and a new digital programmer and room thermostat fitted. They made a nice job and all is fine apart from now that is getting colder, I turned the boiler thermostat up to around two thirds on the knob. My problem is that on about 4 or 5 occasions in the last month, the temperature safety button has needed resetting on the boiler as it has tripped. That's only happened two or three times on the same boiler in the last 20 years.

What I noticed on the old controller was that when the heating water temperature got to near maximum, the boiler would shut off but the pump kept running for a few minutes or more - I presume to allow any heat build up in the boiler to be passed away round the system. Since the new controller has been fitted, as soon as the system switches off, the pump stops too. Also, I have noticed that if the room stat is set at say, 22°, as the system is warming up, often it clicks off at 21° and 21.5° for a few minutes and then clicks back on again. It never did that with the old controller - it would just keep going until the room reached the temperature it was set to. I'm assuming the pump stopping and thermostat switching on and off shouldn't happen?

The plumber was great but the electrician they sent round to connect all the electrics up was bloody useless - a fat wheezing geezer claiming to have flu and he wouldn't get up in the loft where the boiler was to check out the boiler wiring - the plumbing company sent an apprentice round to go up in the loft and shout out what coloured wires went where. Still he couldn't sort it out so they sent another electrician round who got it going in minutes. Whether he checked all the wiring or just did enough to get the boiler firing up, who knows?

Before I call them back, does it sound like it could be wired up wrong or is it just a coincidence that this is happening? Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

Does sound like they've muddled something up there. The pump should run on after the 'demand for heat' has switched off to protect the boiler

Not sure if this helps https://www.worcester-bosch.co.uk/files/tr...ller_3.pdf

The boiler is independent of the thermostat in effect, though the thermostat switches at 21-21.5 unfortunately the read out is not a true reading it is a derived voltage from the temperature using software gain settings. Perhaps the best way is to buy a cheap mercury thermometer and set the thermostat reading temperature cut out point irrespective of the reading. Turning up the boiler temperature does not always make the house hotter this is governed by the number of radiators and their output and the setting of the radiators thermostatic valves, if any, the boiler temperature should be set so that the return water temperature is between 5 and 10 degrees below the boiler temperature setting. You seem to have managed to set the boiler at a temperature above that the pump is needed to work, though depending on your boiler the pump should cut in if integral to the boiler though not if remote unless specifically wired, it may well be that your boiler setting is now very near that of the safety boiler cut out temperature, hence the operation of the temperature safety cut out. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

What I can't understand though is that before the work was done, the boiler could safely be set to maximum temperature without tripping out and the pump definately ran on occasionally when the thermostat clicked off when the room was up to temperature. Now I can't have it set more than two thirds. Could having a sealed heating system have anything to do with it? I know pressurising the system raises the boiling point of water, as in a cars cooling system. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

Sounds to me like the pump over run has not been wired, this can be controled thru the boiler in some cases,but does rely on the boiler having a perminant electric supply to enable this to happen. Sounds like the electrician was out of his depth.  Al C

Having a sealed system has disadvantages, one is that the water temperature can increase unless controlled by a tank thermostat, the boiler uses the tank as a heat sink if it goes into overheat when running the central heating, I suspect either the tank thermostat has been removed or not connected, this can be dangerous as the domestic hot water can boil and scald when a hot tap is turned on, under the old system the overheated water vented into the expansion tank.
The tank thermostat should shut down the boiler not the pump, you need the wiring diagram for your boiler and a sealed system with either gravity or pumped hot water ( whatever hot water water heating you have), this maybe difficult to trace if the electrician has not used the conventional colour coded wires.
Should existing old wires have been used they should have been upgraded by using 17th edition markings at the wire termination All wires carrying current should have brown bands or wires, all neutral wires, blue and earth green/yellow on the 240v system, there are cases where some wires carry no current but only indicate open or closed though these are normally internal and should not be of any of the 240v colours. my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Had a new tank, tank thermostat and zone valves fitted at the same time. Hot water all fine. What's that bypass pipe with a valve on it for behind the pump - didn't have that on the old system?




I think I'll get them back round to check it just to be on the safe side.

Thanks all.  Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

Seems to have been fitted by someone who wanted to exhaust the world of copper and charge an arm and a leg, with all that uninsulated pipe, have you thought about a mini sauna in there  my PC is slightly to the right of Genghis
2012 HSE SD4 In Orkney Grey now gone, best car ever.

Is that h/w zone valve wired up? Al C

Nothing is wired up in that picture apart from the immersion heater - it was taken after the plumber had finished but before the electrician had arrived. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

amerclarke wrote:

Sounds to me like the pump over run has not been wired, this can be controled thru the boiler in some cases,but does rely on the boiler having a perminant electric supply to enable this to happen. Sounds like the electrician was out of his depth.

+1 also on the permanent live - does the boiler completely shut down when the thermostat shuts it off? We have a WB boiler and apart from the quiet hum it produces when running, you have to open the bottom flap to see the green light to say it is running. It has a little blue light that is always on on the front.

I have owned 3 houses so far and in two I have found wiring faults, from silly ones like the front porch light never having been connected or the 3 way valve being wired backwards to our current house where the thermostat on the hot water tank had the wires wired together, effectively bypassing the thermostat. The previous owner said when we visited before moving in that 'we like our tap water hot'. It was! These houses probably had these faults from when they were built. In our current house I put in a proper control box joining the 3 room thermostats and hot water thermostat/timer together and sorted out the faults. Not sure if that helps, but it helps illustrate that mistakes are made... 2016 BMW X3 30d SE in red
MY2013 SD4 XS Firenze Red, 19" 10 spoke contrast paint wheels, Signature Strips, Grand Black Lacquer trim, Cold Climate Pack - gone!
2007 TD4 S Stornoway Grey - gone!

There is a permanent live in the connection box going up to the boiler as well as a switched live when pump is running. Nothing has been touched at the boiler end. When the stats switches off, the switched live switches off, the perm live stays live and both the boiler and pump switch off. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

The boiler temperature will rise as there is no pump overrun to cool it that's why it's tripping the high limit stat the bit in the photo is a bypass in case all the trv, s or other control's shut down it senses a pressure rise and opens so the pump is not running to a dead end so then just runs water round the boiler

Dartman the one wrote:

Seems to have been fitted by someone who wanted to exhaust the world of copper and charge an arm and a leg, with all that uninsulated pipe, have you thought about a mini sauna in there