radiators not hot enough

Now that the weather is colder, I've noticed that some of our radiators are not hot enough, even when the Drayton Lifestyle thermostatic rad valves are up to max. None of them what I'd call really hot. Potterton Prima "F" boiler on 5, i.e. next to Max. Does cut out (in the garage so haven't yet checked out how often and for how long but wasn't firing when I went in there a little while ago) so not underpowered. I took the head of the worst rad as it was a bit loose. The pin was out but I couldn't depress it with a flat object as I believe one should be able to. Put the head back on, doesn't wiggle now but no improvement in the rad temperature. I've checked that there is no air in and the rads are warmer at the top than the bottom. Small bore pipes. The system is supposed to have Sentinel in it so shouldn't be sludged.

Some of them don't turn off even when put back to zero. More than one rad in each room so I can compensate for that. I suspect the pins are stuck but if the pin is stuck out, shouldn't the rad get hot enough?

Any suggestions? Could the pump be on the wrong setting (though we haven't altered it and we were warm enough last winter)?

Very sick husband who feels the cold and unable to deal with this problem.

numerous possibilities . without visiting the property its a complete guess.
if your boiler gets up to temp before rads get hot, it would suggest you have a flow/restriction problem, are the rooms actually cold, have you put all the trv's on max?

when was the system last cleaned or the sentinal additive checked? lots of questions i know.
try turning the boiler stat down a couple of notches, run the flow at a lower temp, that might help, sounds wrong but try it.

sounds like you need an engineer tbh.

How old is the house? Is it Microbore that you have for a heating system?

It is possible you have poor circulation, despite the sentinel. When was the level checked and corrected?


Took a slightly younger boiler than yours out in Hitchin last week and the system was in a terrible state considering its age, despite the Sentinel sticker on the header tank and the feed and vent pipes being plumbed correctly.

Feed pipe totally blocked. Circulation very bad. Took a little while to suss out, but once cleared it all works very well.

Good job considering they were friends of the family and only a few miles from home

Anyway. That was just one solution. But I would be looking towards a sludge related problem.

Thanks for replies. I think the system is about 18 years old when the extension was added; separate system for that end of the house; we have only been here (Bucks, no longer Herts) for 4, so can't tell you when the Sentinel was introduced etc. The heating at that end, which is the part we spend most of our time, is a microbore system. The boiler was on 3 till I turned it up to nearly max. the other day in the hope of improving the rad temperature. Why could turning it back down possibly improve things? Between medical appts. I intend to spend some time in the garage where that boiler is situated to see how often and for how long it cuts out. What should it be? It used to be on and off like a yo-yo but when I was in there the other day it didn't fire while I was there. I had been turning down the rads in the bedrooms during the day to try to save fuel as we seem to have astronomic bills. Can this cause problems? The system at the other end of the house (spare beds and drawing room which we don't use much) has a hall stat and I run that end at a low stat setting. Looks like I will have to get an engineer in but I like to know what the problem is so I don't get spun a yarn or overcharged. Last time I had the boiler serviced, I was told the Primas were better than most of the new ones on the market but maybe it's time has come.

I would suggest your rad valves are causing the problem. However as its been said before poor circulation could be to blame, if you check you F&E tank and see what state the waters in is a good indicator to blow healthy your system is. But more than likely your rad valves need renewing.

If you have thermostatic valves and the pin sticks down you need a new trv. if rads are cold at the bottom and hot at the top, the bottom is full of sludge, hot at the bottom cold at the top air. your system needs new trv's £25/rad supplied and fitted, and a power flush, about £350-£400

Does the boiler make a noise louder than normal before cutting out?

I haven't heard any noise from the boiler when it has gone on or off while I have been in the garage. Indeed it is so quiet you have to be close enough to see the flame come up to know whether it is on or off. The pump is high up above the boiler and I haven't been able to get up to look at the setting or feel if it is vibrating, same with the expansion tank but I will get my garden helper to do that this weekend. If there is no sludge in the tank, can I assume the rads are not sludged up? Certainly some of them get hot at the bottom. It might be the thermo rad valves though the pins are up rather than down. My hunch is that it is the pump but I could be wrong. I will try tapping the valves in the not fully hot rads lightly with a hammer in case they are stuck not fully open. Have had too many hospital appointments to be able to get a plumber in but hopefully that may ease off a bit now my husband has had a surgical procedure y'day.

P.S. to previous:

By the way, which rad valves are the best? My impression is that these Lifestyle rads are not v. good quality. We had Danfoss in our previous house with no problems, apart from on one rad which I was able to fix by tapping, in 35 years.

patagonia said:

Looks like I will have to get an engineer in but I like to know what the problem is so I don't get spun a yarn or overcharged. Last time I had the boiler serviced, I was told the Primas were better than most of the new ones on the market but maybe it's time has come.

Click to expand...

Why do you expect that you are going to get ripped off?

OK there are a few cowboys but most are genuine and have reasonable charges.

You should get somebody recommended by a friend and you can ask about their charging policy before they come.

Tony