Just wondering if it causes any problems if all the rads in a system have thermostatic valves on?

It’s probably not that often that they would all be shut off completely, and even then won’t the pump still be able to turn as it’s just an impeller isn’t it, not like it’s a piston or anything?

A decent modern pump just backs off as they adjust their power based on how much flow they achieve. An older fixed pump just strains a bit until the boiler shuts off as the return temp water is too high. A lot of older systems have a bypass loop, so there is always some flow.

NB All our rads have TRVs on them and the house hasn’t blown up yet….

If you don’t have a bypass you’re at risk of knackering your boiler – even if the pump backs off it’s a bit pointless if all the valves are closed.

Older systems always had a “venting radiator” on the loop. Normally the bathroom one with no TRV on it. Then the system can run at lower output without killing the pump.

Newer systems as above.

What does your boiler manual tell you?Do you have a roomstat?

Our boiler was originally installed (1999) without a roomstat and mostly TRVs. Would occasionally notice it cycling on / off (despite it having an “anti-cycling” feature).

Fitted a roomstat in optimum place in the living / dining area (internal wall, middle of room, away from draughts and radiators) and removed the TRVs in that room – works much better at controlling the desired temperature, less cycling and maybe slightly lower bills as it properly shuts off the boiler once main room is up to temperature. Kept TRVs in bedrooms and kitchen to fine tune localised temperatures (keep bedrooms cooler, turn down kitchen if oven and hob are on).

I put trvs on all ours except one. The one in same room as the thermostat. We’ve got a pretty basic and old system but it seems to work.

Not a plumber but I believe some systems are basically a loop with rads plumbed off in parallel. But the system we have here has a sink rad for the boiler and a rad that should never be closed on the heating (we have a convection DHW system that always heats the single bathroom rad while doing the water and then the CH is driven by a pump off the DHW)

If you don’t have any way to maintain the loop it is bad for your boiler and pump.

If you have a thermostat and a TRV and the TRV is set lower than the thermostat then the boiler then the TRV can shut off before the thermostat so the boiler keeps running which is bad.

Thus you shouldnt have a TRV on the rad in the room where the thermostat is. If you have a moveable thermostat then you can fit TRVs but remember to fully open the one where the thermostat is or you can just unscrew the top bit and put a blanking cap over the top.