My boiler (circa 1985) has recently started to switch off if running the heating and hot water at the same time. It runs hot water for about a minute then cuts off and has to be reset, (push the red button underneath the boiler), this pattern repeats until i stop trying to get hot water. (this happens if running the taps or the shower) (I'm clearly not a plumbing expert and am getting a little fed up of having to get out of the shower to reset it!)
Going off on a safety possible high temp unit needs service such a nozzle filter if oil or thermocouple if gas
SOURCE: Combi Boiler - Running warm & then cold!? HELP!
the problem was solved on my system by replacing thermostatic valve on shower and putting non return valves on hot and cold feed to shower . the problem was caused by cold water getting into the hot water line through the shower hope this helps
SOURCE: Radiator heats up when running a shower.
Your boiler is overdue for a service.
Combi boilers are unlike regular boilers in that they have quite a few moving parts, it's vital that these are serviced annually if you want the boiler to remain reliable and to avoid expensive failures.
In your case, the diverter valve has most likely failed. Normally, when the heating is on this senses when there's a demand for hot water and temporarily diverts the primary hot water circuit to feed the domestic hot water heat exchanger. When the demand for hot water ceases the primary hot water circuit is diverted back to the central heating heat exchanger. The valve has a number of moving parts including a rubber diaphragm which can wear out and split and moving shafts which can seize.
When the valve fails it can leak and also can divert hot water to the central heating heat exchanger when hot water is used. The reason that only the highest radiators in the system are affected is probably because the failed valve does not necessarily cause the central heating pump to activate and circulate the hot water throughout the system (it does on some boilers though). If hot water is introduced into a cold heating system it will rise via convection to the highest points in the system like an old fashioned gravity circulation system which was unpumped.
Call a heating engineer out as soon as possible; I'm not going to advise how to do the repair yourself as gas appliances MUST be serviced by qualified persons only for reasons of safety. If you're lucky then the valve simply needs cleaning up and a few new diaphragms plus other minor seals and rings. If it's gone too far then the valve and possibly the manifold it's attached to will need to be replaced.
In the UK the part alone typically costs between £100 to £200 depending on whether it's just the valve or the manifold as well. The diaphragm kit typically costs up to around £15 and is routinely fitted when the boiler is annually serviced, and a new valve will already have new diaphragms fitted. For a routine service expect to pay for up to two hours labour (many can be done in one hour), but if the valve/manifold have failed it will be longer as one failure often causes other parts to need further inspection/repair.
I hope that I've helped you today, if so please return the favour by rating my answer.
SOURCE: Vaillant ecoMAX 828/2boiler goes on & off when running hot water!
water must be set at 3lts a min ,check diaphragm valve move when hot tap is on, check microswitch ,best of luck
SOURCE: got a gocta w-26mixer shower bar fitted cold tap
from a plumber all hot and cold connections on all major showers are hot on the left and cold on the right just like the taps on your sink or washbowl
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