DIY Doctor UK DIY Forums

Hi,
Since I've had my new boiler system installed, my radiators have not been right. It started when I first switched the heating on in October. The rads upstairs got hot but downstairs didn't. Finally got hold of the engineer and he came round whilst I was at work and balanced the rads. Now, the rads downstairs get hot but upstairs, noticably colder.
Now for the real strange bit. My HW & CH is on a timed system. Comes on at 6.30am goes off 8.30am, then comes on at 4.30pm and goes off at 10.30pm. Apart from the bathroom, all the rads now have TRV's and the thermostat in the living room is normally on 20-21. I have been told that the rads should be very hot on this temp. However, on Sunday when I was at home during the day, I switched the control to Constant. Within 20 mins, all of the rads in the house were red hot! This was on around 21. The whole house got warm so quick. When I switched back to the timed setting for Monday, when I got home, the rads were back to normal.
Please can someone advise me on what I can do so that the rads are the same temp all the time but on the timed setting.

Many reports on this forum have advocated winding the room-stat up to max., and rely on the TRV's.
In my own system, my stat is in the downstairs hallway diagonally opposite a rad with wide-open IRV's, and I select the various room TRV settings for optimum comfort/economy.
I have recently noticed that the system overheats for a while after a shut-down, as I did recently when fitting 2 new ultra-quiet ballcock units in the 2 toilet cisterns (made in USA, and are great).

Thanks for the quick reply. I will try that. One thing I didn't mention is that when the system starts up in the morning, there is alot of noise from the rads, (tapping & banging). It is louder enough to wake me up. I tried leaving the system on constant last night (leaving the stat on 18) but come 1.30 in the morning, the boiler came to life and the noise started. Could this be air in the system, or just water hammer? It never use to make this much noise before the new boiler was installed. The new boiler though, is in the loft, whether that makes any difference. Is there a chance the engineer could have over balanced the rads?
Thanks again

I have read of this start-up noises being due to either (1) air in rad. system, needing bleeding with boiler shut down (pump needs bleeding also, expected to be in the boiler casing, if you have a combi, as you should, and the pump does not like gas/air/hydrogen going thro').
(2) --- boiler flame setting may be too high, causing brief kettling ; --- very bad for boiler life.
My new condensing combi has its gas knob adjusted to give 64 C on DHW, and the other gas knob adjusted to give CH temp of 59--71 C range, during on/off cycles.
The room stat. is set for 26 C, and gives 20 C two feet away, and 22 C in the living room at head height when seated.

THESE NOISES COULD BE AIR OR EXPANSION OF THE PIPES. ANY AIR IN A SEALED SYSTEM SHOULD FIND ITS WAY TO THE TOP OF THE RADIATORS OR THE AUTO AIR VENT IN THE BOILER, UNFORTUNATELY EXPANSION NOISES ARE USUALLY DUE TO PIPES RUBBING ON THE JOISTS OR AS THEY PASS THROUGH THE FLOOR BOARDS, USUALLY MORE NOTICABLE UPSTAIRS IN A HOUSE

TRVs:

You mention that there are TRVs everywhere except the bathroom. If there is a TRV in the same room as the thermostat there will almost certainly be problems. As the "thermostat room" warms up the TRV will gradually close to reduce heat in that radiator - that will cause the room to then cool. As the room cools the thermostat will "call for heat" from the boiler. The overall effect is that everywhere else in the house will just keep getting hotter and the temperature in the "thermostat room" will fluctuate as the TRV and the thermostat "do battle" over the room temperature. The thermostat should not be in the same room as a TRV.

Noise / New Boiler:

It is possible that the new boiler is heating the water in the central heating system much more quickly than the old boiler - this often leads to rapid expansion creaks and noises from the radiators and the pipes under the upstairs flooring. Most modern boilers have at least two gas pressure settings - one for the central heating and one for the domestic hot water (in the case of a combi system). I fixed the same problems by:

- reducing the gas setting for the central heating so that it was more "gentle". (The system took slightly longer to warm up so I adjusted the start times by 15 minutes.)

- using small (cut up) sections of foam pipe insulation on the upstairs pipes to stop them directly touching the joists or the underside of the floorboards.

Thanks for the replys.
As previously posted, I stated that when the heating was on timed, the rads didn't seem that hot to when it was on constant. For the past week I have noticed that when the HW switches off at night 10.30pm the CH which was on constant, all the rads suddenly got really hot. So I did a test and switched the HW off for in the morning. When I woke up, the rads (set at 20) were all hot! Is it possible that the HW is taking the pressure/power away from the CH? Just seems strange that whenever the HW is off and the CH is on, the rads were fine.
So much for having a new boiler, my old was more reliable!

I take it that your "new" boiler, is not a combi, as that has DHW priority, when flow of > 2 litres/min hot is being asked for. That being the case, your diverter valve is unlikely to be new, and looks to be a likely suspect. A ruptured coil in the indirect hot cylinder is another.
If the new boiler IS a combi, then it needs to be more than double the output of an old vented-system boiler, as it is dedicated to DHW every time a hot tap is in use, and the rads. need some REAL heat to recover from the down-time.

Are you sure the TRV is not wrong way around? Some will work either way but other have to have flow in right direction if not as they reach temp they are set to they start banging.