My boiler heats the water but is not firing for central heating-new boiler

No gas pressure will not be affected by your meter. its a heat sensor problem .

Combi-boiler-turn hot water tap on/off and the heating stops for ...

singletrackworld.com/.../combi-boiler-turn-hot-water-tap-onoff-and-the-...

Combi-boiler-turn hot water tap on/off and the heating stops for 20secs ... hot watertakes priority over central heating so when you run the hot tap, heating is ... Yeah onmy worcester combi there is a diverter valve - it feeds either the heating or ...

My central heating works but I have no hot water - 24'7 ...

https://www.247homerescue.co.uk/my-central-heating-works-but-i-have-...

Diverter valves switch heat between the hot water and the central heating. When youturn your hot tap on, the diverter valve temporarily shuts off the water supply ...

Does your boiler keep switching itself off? Here's why ...

www.dhs-uk.com/does-your-boiler-keep-switching-itself-off-heres-why/

Jul 7, 2015 - ... Bathroom Suites, - Showers, - Wet Rooms, - Taps and Accessories, Information and ... Low water pressure can cause your boiler to turn itself off. ... boiler is not turning off, you aren't getting the amount of hot water you require. ... If there is air in your central heating system, then your boiler may shut down.

If this is in a RV the propane monitoring valve may require more gas flow to turn on than the water heater requires. A central heating system requires substantial gas flow so when the monitoring valve opens to fire the central heating, there is enough gas flow to also fire the water heater.

you should have a programmer that will let you have the hot water and heating on or off . You could have a motor rised valve on the system which controls both . depends on what system you have . Fully pumped of just pumped on the heating side .

There is a flow sensor in the circuit and it is not sensing the lower flow from just the hot water. When you put it on heat though it does.

It could be dyslexia, but I think you want to know what may be wrong with your boiler in this case!
This is a VERY old design. The diaphragm is on the water section, this operates a switch to turn ON the pump, and a further device causes the diverter valve to divert boiler water from CH duty to HW duty.
From your description it appears that the boiler is shutting down on internal boiler water temperature (too high), your 'briefly too hot' HW symptom may be caused either by the boiler side of the secondary heat exchanger being blocked/caked in sludge, OR the DHW side of it being scaled. Either way a new or replacement (descaled) secondary heat exchanger MAY inprove things. It's not easy on these old clunk-pots, and EVERY disturbed seal will subsequently leak, so get a good supply of o-rings and fibre seals before you start ("you" being the competant fitter you employ)

Hi,
In most cases problems with the circulator pump boil down to two problems.
The most common is air in the lines causing an air lock.
The next problem is that the pump gets stuck and is not running even though itmay be hot and seem to be running. In this cause the pump can sometimes betaken apart, cleaned and it will work, but usually it needs to be replaced.

Here is a tip that I wrote that will explain circulator pump problems in moredetail.

Heating Circulating Water Pump Problems

heatman101

back boiler run from a gas fire? check the instructions to operate the gas heat to the back boiler not just the fire
I presume that this a fully pumped system - air lock doubtful There maybe on/off valves on the pipes to and from the back boiler [situate close to cylinder] make sure they are on - anticlockwise turn
or there could be a blockage in the outlet from header tank usually in the loft. or If there is no water in it maybe the mains cold feed it is off.
Note if no water in it DO NOT USE the back boiler

what size of gas line is going into boiler and water heater? is it black iron ? natural gas or propane? have you checked gas pressure at water heater and furnace ? if they work fine individually then you have a problem with incoming gas pressure. Call gas company and ask them if they would come out and check gas pressure.

vailant boilers are one of the best on the market and should last you more than 6 years depending on installation and servicing.
the engineer you had should not have replaced the diverter valve if the boiler was firing up when the taps are opened. if you was getting luke warm water with the boiler alight it is a classic symptom of a blocked plate heat exchanger on the central heating side.
a new heat exchanger can cost around £100 depending on the age and model of the boiler.alteranatively it could be descaled but may clogg again. it would be a good ideal to fit a magna clean filter on the system to help prevent further debris if you have a dirty system .if you don't trust your engineer i suggest you ask another. find out if he is registered first and don't pay until you are satisfied with the work. if you are asking the same engineer back try and get a discount off the work as he has failed to rectifiy the original fault and fitted the wrong part due to wrong diagnostics. if he is registered you can complain to the governing body ie corgi or gas safe register.
good luck.