Two radiators not heating

[simbo69]

Hi all, looking for any help, advice, experience please!

We had an extension built, which added three radiators and required the boiler to be moved further towards the back of the house. Since then our hall radiator has never really worked and then this winter the cloakroom rad has also stopped heating up - these two are at the furthest point in the house from the boiler.

Earlier this week we had the system power flushed (loads of sludge was cleared out) and balanced and initially the cloakroom came back on and the "flow" pipe to the hall rad heated up but didn't really warm the rad.

The next morning I got up and noticed that all the rads were warm, I then turned up the heating thermostat and all of the rads warmed up including the hall so we thought it was problem solved. However as soon as the shower was used two or three times and the boiler had to start heating hot water both of the problem rads cooled off and have stopped working again.

Last night I turned off the two rads in the rooms above the hall/cloakroom and straight away the hall & cloakroom did start to warm again (so assume there is no new blockage in the pipes) but as soon as I turned the others back on they cooled off again.

The plumber who did the flush & balance is being very helpful and making enquiries for us but I thought I would put it on here to see if anyone else can shed any light. Our two trains of thought are a) is the pump in the airing cupboard not man enough to heat the whole system now its been extended or b) is the boiler struggling to run the bigger system (its a Potterton Prima F40, 20+ yrs old but working ok, located on the ground floor and being asked to run 5 rads upstairs, 7 rads downstairs plus hot water).

Any thoughts gratefully received

 

[oldbuffer]

1. Don't know what pump it is, but most should run 12 radiators over two floors and the hot water cylinder.
2. Your boiler's maximum output is just under 12Kw. It's probably only just man enough to run the heating but not the hot water at the same time, depending on how well insulated the property is.
3. Try setting the programmer to make sure that heating and hot water are not on at the same time. Say an hour on hot water just before the morning heating, then another hour before the evening heating with perhaps an hour's boost at midday.
4. Maximum loft insulation could make enough difference to run both at the same time.

 

[McCombi]

I would day undersized too.

Maximum output in boiler is 11.7kw, without seeing all radiator sizes difficult to say for sure but if alot of double panel ones and big rads, boiler has no chance of heating them all and hot water cylinder also.

Might be worth getting an rgi to confirm boiler is rated to its maximum srtting also

 

[JohnD]

is the boiler running flat out, continuously, yet unable to get all the radiators hot while also trying to heat the cylinder? Or does the boiler run intermittently?

Are any of the rads fully hot?

Do the rads warm up after half an hour or so, when the cylinder is getting hot?

 

[simbo69]

Thanks for all your replies... Your comments do seem to indicate that, as we suspected, the boiler may be under-powered now we have extended the house - from memory it was all working fine before. One other thing that I forgot to add is that part of the extension included an en-suite to the master bedroom which is still waiting to be done and of course we will be expecting to add another heated towel rail (plumbed) putting more strain on the system!

In reply to your questions/comments:
1) The insulation has already been added to with the entire loft having had a whole new layer over-laid across the original, the extension is of course packed with insulation - cellotex to varying thicknesses in walls, ceilings, floors etc. and so I'm not sure there is much more we can do to improve that.
2) Its a Grundfoss pump and has been set to the highest speed(?) on the advice of another gas engineer we spoke to.
3) There are varying sizes of radiator but all of the new ones were double panel, purely because of the sizes of the rooms and open areas that were created, other than that there are a couiple of biggish original rads and when we had the bathroom re-fitted replaced a rad with a tall heated towel rail.
4) Not quite sure on the running times of the boiler but most of the radiators do achieve full heat and most of the time it is just the two in the hall/cloakroom that do not heat at all - before we had it flushed and balanced last week I always found upstairs to be almost too hot but that has improved after the balancing.

I have left a message with a Gas Safe engineer we have used before and will get him to come out and give us his thoughts, but I think we are now expecting it to be a new boiler

Thanks again for all your help!