My rads aren't heating up properly and my house is cold

[toomuchlikemyusername]

Hello can anyone offer any pointers please?
Worcester Bosch boiler. Hot water tank in airing cupboard. Rads throughout property with TRVs fitted.

This autumn I've become aware that the house isn't warming up properly. Rads are generally luke warm and temp is struggling to reach anywhere near 20+. Boiler is firing up but then seems to cut out soon after. Serviced 14 months ago.
Mid point valve was replaced about 18 months ago and seems to be moving when heating/water is turned on/off.
Room stat has new batteries and moving it around the house seems to have no impact.
Rads have all been bled.

Any advice would be appreciated before I call in the heating engineers.

Many thanks.

50 is OK. The water at the top of the cylinder (where it comes out to go to the taps) will be hotter.

If you have a thermometer you can test the tapwater. I think you will find it approaching 70.

Fiddled with valves would be some Central valves rather than just a radiator valve. But if the system was partly drained something could have been closed and not opened properly. Or something could be open that's not supposed to be as piglet John is trying to check

@johnd2 no, I'm not aware that any central valves would have been messed with.

@PigletJohn I've done what you suggest re the pipes and I'm reporting back that in both scenarios, all three pipes are very similar temperature. I've also noticed that they are cooling down and heating up again each time to boiler fires up and shuts down. At their hottest they are too hot to hold for more than an instant.

OK

If the pipe to the cylinder is getting fully hot, even when the HW is set to "off" then the 3-port valve is letting by. Usually it is due to internal wear, but it can be a fault in the motor or wiring.

Sad to hear that you had it changed not long ago. Do you recall if they just changed the motor head, or the brass valve (involves draining water out) as well?

If the pipes are getting hot so quickly I do not think the pump is at fault.

Ask the boilerman to clean out the Magnaclean which is the black plastic tub tucked behind the pipework. If there is a lot of black dirt in it, that could be one reason why the valve wore put so quickly. If there is brown water you have a worse problem with dissolved air in the water. The Magnaclean is rather tucked away, I don't know if you can do it yourself. With an open vented system like yours corrosion is more likelt to occur, but it is also fairly easy to do a DIY clean if you wish. maybe leave that till summer, though.